Usually the only Enkis I see there are the newly-spawned ones, who don't exactly know their way around and just spend their time attempting to kill rats with their bare hands. A lot of times I stick around Oja just to help them; give them trias or weapons or show them around (oh yes, I'm such a good Samaratin). However, once they learn the way to Hydlaa and see how much bigger it is, they fly the coop and only come back to sell their hides.
A little while ago I saw an advertisment for a player buying rat hides in Hydlaa to lessen player's trips, who would run them to Oja in return. I think it's a great idea, but that basically eradicates, for most players, Oja's one big service. The only other thing I can think of that is truly unique to Oja is the NPC that trains Body Development, which is supposedly a working skill but I don't know how it works.