Now that we have established the basic situation in the Kreetan Narrows in the previous post, it's time to see what Wookiepedia has to say about the Suolriep Sector - and what we can extrapolate from it.
First of all, the sector is described as "desolate", and only having "light traffic". Why is it desolate, though? Is it just because there are so few star systems - or do ancient evils hide here that even the Hutts were loath to disturb? I haven't read up on the ancient history of the Star Wars Galaxy ("The New Essential Chronology" is lying on a table nearby, waiting to be read), but ancient Sith ruins and the like would be great for both treasure-hunting adventures and stories revolving around the Force (I expect at least one player character to become a Force-sensitive because, well, there is always one).
The entry also mentions that the sector is the location of the Rebel Alliance's Delta Base. Sadly, the entry is a bit sparse on what Delta Base is all about and the sources cited refer mostly to long-out-of-print West End Games supplements - but on the other hand, this means I can feel free to make stuff up.
Some things can be inferred, though. For starters, the base gets an influx of new people soon after the Battle of Yavin (which is still a bit in the future at the start of the campaign) - most notably among these is one Vanden Willard. Who was actually the military commander of the forces at Yavin, and who subsequently won another important battle for the Alliance before taking charge of Delta Base. Considering that the Alliance is chronically short on capable people, much less competent commanders, I can only conclude that Delta Base is a very important base for them.
Delta Base was established on the moon of New Kisge - apparently by Willard before the Battle of Yavin. So maybe he used his newly-won prestige to vastly expand the base - making a good argument that it would be an ideal location for basing future operations from. New Kisge is also the homeworld of the near-human Samuac (whose only difference from humans is apparently their red eyes, allowing them to see in darkness), who "managed to avoid subjugation by the Galactic Empire". In fact, the whole moon - which has "dense undergrowth-covered wilderness" - has "escaped the attention of the Empire".
Zooming out, New Kisge is the eight moon of the planet Chaasch (presumably a gas giant). Chaasch is located in the Suolriep System... which also includes the planet Suolriep, the sector capital!
Wow. So apparently there is a near-human species living on a habitable world in the same planetary system as the Imperial Sector Capital - which has got to be one of the most populous and highly-trafficed worlds in the sector - and yet somehow the Empire doesn't even notice them! No wonder Willard thought this would be a great place to hide out!
So, how to explain this? Well, let's start by assuming that Chaasch is generating fierce magnetic storms which scramble all sensors (which are especially harsh on unshielded ships such as TIE Fighters). However, that won't be sufficient to hide all traffic in the area, so there is also a massive and ancient mining station that extracts resources from other moons - and which has been throroughly subverted by the Samuac.
Speaking of which, the Samuac are listed as having the "Samuac Tree Code" as their native language, which doesn't exactly speak of "high-tech civilization". But let's try this: The "undergrowth" of New Kisge is actually a single plant system, like the Pando Aspen Tree but on a planetary scale. The Samuac have learned communicate through this plant, allowing them to maintain a largely coherent planetary culture despite their low tech level.
Then, maybe a thousand years ago, a group of human smugglers landed on this planet and discovered the natives. The natives learned of the dominion of the Hutts and decided that they'd rather stay hidden for the time being. The smuggler rather liked having a hiding place that the Hutts didn't know about, and concurred - and a profitable bargain was worked out. The smugglers gradually introduced high technology to the world, which the Samuac only used in underground caves (which were gradually expanded to entire underground cities) in order to avoid detection. A crucial piece of tech was the introduction of cybernetic eyes, which the Samuac could use to pass for human. Selected agents were sent to the world of Suolriep (which had been settled by humans, among other species) and gradually arranged for the construction of Chaasch Station, the aforementioned mining station.
Of course, sooner or later the inevitable happened and the Samuac agents sired or gave birth to children with human partners while being offworld - and some of these had their Samuac parents' red eyes. It was decided not to automatically tell these children of the truth about their heritage in order to protect secrecy. Gradually, a story spread that the rays of Cardai (the sun of the Suolriep system) gradually mutated humans until their children were born with red eyes - which is total bunk, of course, but the Hutt overlords of the region were not interested in any scientific research that didn't promise future profit, and so the story survived. Now "red-eyed humans" are called the "Children of Cardai" and have spread across the sector - further confusing the truth about the Samuac.
Of course, eventually it was discovered that there were people living on New Kisge - but the Samuac simply pretended that they were the descendants of shipwrecked human survivors, and that they had no interest in leaving their dark, overgrown, monster-infested hellhole of a world and that any outsiders should just leave. Outsiders who couldn't take the hint suffered attacks from the native fauna or otherwise suffered from "accidents", and thus the world was largely left to its own devices.
The Empire, once it showed up, didn't bother with the world either - like later events on Endor showed, the Empire doesn't bother with crushing primitive populations of worlds that don't have valuable resources to exploit and do not pose any other threat to its interest. Chaasch Station paid its tribute, and reasonably on time too, and that's all that mattered.
Then, somehow, Willard ended up on New Kisge and won the trust of the Samuac. I imaging a grand tale of the Planetary Romance style, which likely involved him marrying a native princess (which always seems to happen in these kinds of stories). He convinces them that opposing the Empire is worth risking an end to centuries of secrecy, which must have required some truly spectacular heroics. And thus, Delta Base is born, with Chaasch Station serving as a cover and the Samuac agents abroad providing additional intel.