Hey Tom, nice guitar :)
I did a lot of research into whether Hercules hangers (and other brands) would mark nitro when I had my SG faded. Basically, the consensus from various forums was "I wouldn't do it", while those who actually had used Hercules with their nitro guitars had had no problems. I heard no horror stories about Hercules; only about those cheap and nasty floor stands, where the foam rubber basically comes apart in your hands after a year or so anyway. Understandably, Hercules themselves were reluctant to guarantee that their foam rubber is nitro-safe, because there are so many different sorts of nitro, but they did give the impression that odds were that it would be fine.
I know all of that amounts to very little certainty, but it might save you some legwork coming to the same conclusions. Personally, I'd hang it, but I wouldn't really be concerned by some discolouration, so the utility of the hanger would definitely outweigh the risk for me. YMMV!
I'd imagine that putting cloth over the contact points would actually increase it's security, since it'd effectively make the guitar thicker and less able to squeeze through. Just make sure not to foul the little holdy-mechanism-thingers, 'cause that would stop the hangers operating correctly.
