Both Remus Lupin and Fenrir Greyback were werewolves. If Wormtail had grabbed onto to one or the other with his silver hand, would the magical hand have disabled or killed either werewolf? Would it depend on which part of the body grabbed onto? Or in traditional werewolf lore is silver touching against any part of the body enough to be debilitating or lethal?
JKR was never very clear on this but she obviously was aware of silver connection.
From http://www.jkrowling.com/textonly/en/rumours_view.cfm?id=38 (retrieved via Wayback machine):
Peter Pettigrew's silver hand will be used to kill Remus Lupin
JKR: Nice idea, clearly predicated on the legend that only a silver bullet can kill a werewolf – but incorrect.
Now, this may be parsed in 2 ways: as "incorrect because silver hand is no threat to Lupin" for whatever reason, OR merely as "No, Lupin will NOT be killed by that hand, independently of whether he can be".
On a side note, one can also not read anything unambiguous into the "silver hand" word choice (as opposed to silver haired hand) - elsewhere in the books she uses "silver doe" to mean silver colored doe.
One consideration that would indicate it's not real silver is that the hand made out of actual silver would likely be a bit too heavy to be useful.