you can get STD's from Oral sex...

AIDS, HERPIES II, HERPIES I, Goneria, Siphilis, etc

The viruses will often go through your glands in your mouth... I dont know what diseases will go through these... the bacteria based ones (Goneria, Siphilis) might be less likely during oral sex... and the data for AIDS and others is mixed. Some say its MORE likely, other less...

You could use "Dental Dambs" which are big sheets of latex that you lick which is placed on the vagina... but I think I would rather not even participate then attempt something as horrible as that must be.