Can an Engine run on an engine test stand with a Holly sniper FI unit?

Dyno, yes. Engine stand, probably not the best idea. Modern dyno shops are equipped to handle EFI but an engine run stand is pretty basic and really doesn't have the peripheral equipment to facilitate it. Run stands don't put a load on the engine either so it's not really a true break-in. But mostly, if you're not familiar with EFI, first fire up is really not the time to learn about it.

You'd want to have the electrical stuff planned out to simulate how it would be set up in the car which is a project in and of itself. EFI needs to wired properly or it will have problems. Temporarily twisting wires together in attempt to get the engine running is not the right way to go about it.

You'll also need a fuel delivery system that can supply sufficient pressure (58-60psi). How are you controlling the ignition? It's generally best to control the timing through the Sniper so you'd also need to have that set up beforehand. That part is not a huge deal but it is a consideration.

Kind of a long-winded way of saying put a good carb and ditributor on it to make sure it fires up and runs right away. Once it's in the car and running, then put the Sniper on it.