I know it won't move, but will the engine still start up or is there some safety feature in place?

 

I don't see why it wouldn't start...

 

It won't start if you sheared off the flex plate. That would give you the impression the TC was blown for sure.

 

It won't start if the torque converter has ballooned out into the bellhousing either, only seen that once though, on a th400 in a motorhome. But you could always try to unbolt the TC from the flexplate and see what happens.