I'm watching salsa dancing on ESPN2 right now. I wouldn't talk anybody out of doing this professionally, unless the dance partner is a blood relative. Part of the appeal of watching salsa dancing is the 20% chance that the two dancers suddenly get so hot and bothered by what they're doing that they suddenly rip their clothes off and start humping on the dance floor.
That whole thing goes away when watching a brother and sister team. The standard move of the man sexily sliding his hands up the sides of his partner, thereby lifting her dress above her underwears briefly... that move takes on a whole other meaning when it's sis and bro.