It's cool coming up wirth alien species to populate a universe, but for the purposes of a cantina setting, they need to be able to interact meaningfully with each other. If their biology is so different that they can't breath the same air, drink stuff that can be served at the same bar, have some means of maniplating objects, and a means of communication that won't cause communication issues, they can't be used.

The purpose of aliens races in SF (and fantasy) after all, isn't to showcase odd biology, but to examine the human condition through social interaction. A race of 20-foot tall reptilians may be cool, but has no real place as a PC race, due to the fact that the size limits meaningful interaction with others. Star Trek's Tholians present a similar obstacle due to their need for heat.