Yes, it is perfectly fine and totally acceptable to ask someone of the same gender or sex as you to dance. Same-sex dancing, regardless of actual sexual orientation, has been a part of the dance scene for many years. It is becoming an increasingly more significant part of the social/nightclub life as more couples feel comfortable to open themselves up and break from the traditional man-woman partnership that there has traditionally been in partner dancing. Many nightclubs in the Bay Area especially don't treat their same-sex couples any differently, and no one bats an eye at two women or two men dancing together. Everyone is just there to have fun, and in the end, it doesn't really matter who you dance with as long as you both have a good time!