I recall a viola player turning up with a few friends at a session and playing a whole series of sets which they had obviously rehearsed, a fifth lower than normal. Evidently, they expected everybody else to fit in with them rather than take the trouble to learn how to play the tunes in the usual keys. This was not popular among the other musicians! The viola can work very well indeed in dance music (I make no distinction between -for example- Irish, English or Scottish except in terms of detail in playing styles) but it needs to fit into what's already being done.

Unfortunately for the viola player (and I've tried it myself from time to time, albeit on borrowed instruments) that does sometimes mean using fingering which is a bit more difficult that what the fiddlers are doing. I think it's worth the effort, though.