Very few girls in the brothels use condoms for hand relief.
Condoms are used by most working girls in establishments for oral and I personally recommend them in sex work.
Interestingly the Aids council do not recommend them for guy to guy oral in the private world, because they say it is to restrictive and to get most using them for penetration sex works better this way.
Is there much threat from HIV spreading through oral.To date I have never seen any conclusive proof of this but I have been told it has happened.
More importantly, Genital Warts, Claymida and Gonerah are more commonly passed by oral with out a condom.
A very well trained sex worker can check for these conditions and therefore reduce her risk and therefore yours, but unless she does a proper penis and fluid check I would never recommend to take the risk.