There does seem to be a dearth of different information regarding the risks of acquiring HIV via oral contact.
To be fair most just er on the side of caution, which is no bad thing. The risks do seem very small from the available research done. In the end its down to judgment and whatever you feel comfortable with.
This link seems to provide a decent level of background research into the issue.
http://www.freedomhealth.co.uk/blog/2009/02/can-i-get-hiv-through-oral-sex.html
I don't think HIV is the main area of concern, given that most people accept the risk from performing OWO is miniscule provided the giver practices good oral hygiene and does not have cuts/lesions in the mouth, bleeding gums and so on; according to my GUM you would still have to be phenominally unlucky to be infected this way and I don't believe that there is a single case on record where this has been proven beyond doubt to have occured.
The main concerns for me at least are herpes, chlamydia and gonorrohea - all of these can be picked up far more easily and the latter two may have no symptoms. That said, I've been giving OWO as girlfriend or prossie for over twenty years and I have never caught a thing. Dentyl mouthwash is alcohol free and good as a breath freshener (and I like Smints too - you can chew one after rinsing your mouth with water following a sesh). Listerine is very alcoholic and I particularly like the blue one; there is also Corsodyl which contains chlorhexine (a strong antibacterial) but this should not be used often as it is really a treatment and prolonged use thins the skin inside the mouth.
I don't have an answer as I use a combination of all of these things as well as brushing and flossing religiously to keep my gums healthy and guard against any entry points for infection. My clinic don't like me doing OWO either but they have never mentioned mouthwash, just not doing it at all!