Nichelle Nichols can sing because she used to work for Duke Ellington in the years before TOS was on the air, but she's one of the few TREK actors with pipes.
I would have liked to hear her sing. I think she did at one of the convention parties this year, but I was downstairs watching the Connor/ Dominic comedy show (or the ConDom show as they referred to it!). Upstairs Susie... oh heck.. I cant remember her last name.. she played a Klingon.. the mother of Alexander.. she sang. Avery Brooks also sang at the convention as did Nana Visitor. Maybe there were others, but those are the only ones I remember right now.