I'm outraged, on both your behalf and the cat. Do you know why it's not neutered? This is why it has AIDS in the first place of course, and continuing to not have it neutered will mean it's spreading it to all the other cats in the area.
DSis's cat did that to my car (and I couldn't believe the gallons of wee that poured out of him - he must have been holding on for hours), and I never did quite get rid of the smell. I ended up selling the car (with the help of copious amounts of air freshener).
No it won't be a risk to your neutered ladies. If it's just been under anaesthetic it would have been a five minute job to lop its balls off at the same time. I'm really surprised the vets didn't insist on it given its FIV status.
It could still be done now. It can be done at any age.