The Cult isn't really essential for an adventure hook (although perhaps it could be), but it's the only real religion that's native to the area, other than the Sisters of Ginh Tanh, who don't have worshippers, so it would be nice to have it present, to add local flavour, rather than one of the more generic religions. I think that if there are enough Lotana in Rapata to have two or three Cult temples, than there's a good chance a local village may have enough for a temple, although not a village to the east of the city, going by the sourcebook. For the local priest to be a member of the Cult, a significant Lotana population would appear to be needed, so I would assume that in a small town that could easily mean Lotana-dominated. Of course, that could merely mean that they are the largest minority, with no one race having a majority. Or do we have more than one major religion in the town?