A virgin teenage Succubus IS rather odd...but since Kurumu has already decided to make Tsukune her 'Destined One' aka 'mate', she won't do that to him - any other guy may be fair game to that though.
Besides, with Moka surviving on tomato juice and medical blood packs instead of ripping into a human whenever she gets hungry, I'm sure that Kurumu has a way of keeping the 'soul-sucking' urge in check.