I'm not a wholesaler - I'm a retailer. I handle livestock daily. Other than washing my hands and being careful about myself I don't take any special precautions. I'm also aware of many of the potential hazards - toxins, infections etc. And I guess I have a pretty good immune system.
One thing I do take care of is if I'm working in a tank, I make sure to remove any salt creep around the top of the tank before I start working in it. A common problem that seems to arise is that people expose their upper arm to potential infection by not doing this. You're in there scrubbing algae, your arm is rubbing around at the top of the tank against the salt creep. The salt roughs up your skin and opens the door to infection, next thing you know you've got a big rash. It's a simple thing to just make sure you're not roughing yourself up.
As for handling live rock and such, I think my hands are tough enough now that they don't wound easily. I've been stung by bristle worms so often that it's barely an annoyance now, unless they find a new spot on my skin that hasn't been stung before
My biggest fears are toxins from zoanthids and palythoa - I rinse my hands very carefully after handling them, and stings from venomous fish - and a healthy respect of those is my best defense.
I did get a nasty bite last fall from a viper eel. Broke the skin, I bled like crazy. The skin healed in a few days, but the wound showed signs of infection a week later, and swelled up (no eruptions of the skin, it was all sub-cutaneous). I showed it to my doctor a few days after the swelling started, but by then it had started to subside. Doc said I appeared to be winning the battle over a minor infection on my own so I did not get antibiotics but was instructed that if it got worse, to see her for some. It went away on its own.
I know that there are some infections that are really nasty and require months of painful treatments - I guess we're all vulnerable to them, but thusfar (knock on wood) I've managed to avoid any major problems.
The problem with gloves is that water will get into them anyway - and unless you've got some heavy duty gloves, live rock will shred them pretty fast.
Being aware is half the battle I think - being careful too.
Jenn