I once used a hand from the newer plastic GW Skeleton Warriors as one clawing from the ground on the base of a necromancer raising the dead. It was open and I just bent it open some more.
I couldn't tell which exact hand it was though.
The open hands of Mantic Skeletons are not detailed enough (blank insides), so wouldn't recommend them. On the command sprue though, there is one Skeleton bursting from the ground with its hands up, so those are well suited for your purpose.
The Wargames Factory plastic Skeletons are pretty detailed, but rather slight, compared to the other two (especially GW
) and the insides of the hands are also rather bland.
However; if the hand is to be based on its own, I'd recommend using something more bulky and metal, if only because of sturdiness; plastic and resin hands would just be too fragile on their own I fear...