Depending on the club and the situation, I could well point out that we have folk spots not classical pieces, perhaps ask if they did anything in keeping, etc. yes.

And I've yet to hear of anything describing itself as a folk club that is truly open to everything musical. Perhaps one might draw the line at heavy metal, classical seems to me a good one at getting people complaining "it's not folk", and oddly enough I've found this sort of thing with people who themselves claim to be open to anything...