Using a Ice Crusher for frozen Tomatoes

Agree with Nancy, I'd let them defrost enough for the skins to easily slide off, then pulse them slightly in a food processor in batches, just enough to chop/dice them. I'd probably also allow them to sit in a strainer (collect the juice) so your salsa isn't quite so juicy... freezing tomatoes causes some of their cells to burst making them juicier than fresh would be.

We let them defrost. The skins fall off as they defrost. Then, when they are defrosted, we run them through a food mill.

Not sure, but I would be concerned about cleaning the ice crusher after passing the tomatoes through.
Could you perhaps partially thaw them, then run, in batches, through a food processor, blender or food mill to make the salsa?