Is the use of a hand held sports vibrating percussion massager safe to use on back during pregnancy? my wife is currently only 7 weeks pregnant.

Best avoided: It may be safe, but probably better to avoid it. It's almost impossible to do studies of these sort of things. I doubt it would strike hard enough to do damage, but it's never a good idea to subject a pregnant woman to too many vibrations or hard knocks, due to a very small chance of tearing the placenta. Odds are, she would be fine, but why take unnecessary risks?

Sure: Yes it should be perfectly safe! just don't hit her with it ;-) seriously though, there should be no risk from that tool or massage on general. In fact, it can be very therapeutic!