Several things:
Regarding possibility of mast bumping at the top of the zoom climb - it's going to be pretty difficult to generate a lot of negative G at 60 knots, unless you slam down the collective. But the collective at this time in this maneuver will be on the bottom, so all you're left with is the cyclic. Just like you couldn't generate 2G (1 more than you already have) at 60 knots with only the cyclic, you'd be very hard pressed to get down to a G level that's going to make trouble.
Of course, one hopes that the pilot has been properly trained in the whole art of flying helicopters when doing this sort of thing.