I was actually serious, wonder whether it is unhealthy or not, since the last few dozen posts have been about diseases and stuff.
Lesbians have the lowest STD transmission rates because oral sex on a woman is one of the safest sexual activities.
No, vaginal fluid will not hurt you, you could pick up a STD if you don't use a dental damn in theory, but the transmission rates, again, are low. Still it's a calculated risk, you should probably learn about it yourself before you decide. This is the most easy to understand chart I've ever found: http://www.sfcityclinic.org/stdbasics/stdchart.asp
It's not hyperbolic, either, which is nice for a change.
FYI, the easiest thing to pick up this way is probably HSV I or II (herpes), but considering condoms won't even protect you from herpes, you should just know what an outbreak looks like and avoid going down on someone who has one. Transmission rates from a person using medication and who is not having an outbreak are pretty low.