At some point the question of HIV status will come up. These days poz guys aren't looking to infect anyone and are honest about their status, in my experience. When I have had sex with a poz guy he was more nervous than me. If a guy told me he was negative I wouldn't have him wear a condom if I went down on him. The virus would have to come in direct contact with an open cut (in your mouth, or elsewhere) and unless you've just brushed your teeth, flossed or had dental surgery that's fairly unlikely. So no, I wouldn't.