It's one thing I think DS9 always did, fleshing out the universe with weird and wonderful aliens who you (unfortunatley) never got to see. One of the benefits of being a station, the sheer varitey that passes through the airlocks.
There was also the episode where (in conversation) there was a two-headed alien who could never make up his/their mind (think it might have been the one where Odo and Curson bonded).
Ok, so no Betelgeusian Vilix'pran. Just something else, even more interesting.