I love BBBJ but if a gent wants CBJ, I don't have any issues doing that for him.  I keep Durex flavored condoms on hand just for those requests.

I've been doing BBBJ for over ten years (8 of those as a civvie) and I've never had any STDs in my mouth or throat.   Its never been an issue.  

There is a risk in everything we do.  Only way to totally not risk STD is to abstain completely.