Put in a drain for what? Washing cars? My cities dont allow drains because of envirnmental concerns. You would need to cut up the floor and trench into some sort of cistern or tank. I believe thats a very big deal and I doubt you could get a permit for it anyway.
Slab heat in the garage huh..thats pretty cool. I live in Mn and my floor hasnt flaked in 24 yrs, however I have numerous "pops" that are caused from shale being in the cement mix. I think your cement guy is trying to pass the blame.

Most concrete people will tell you salt will flake concrete. Gotta blame someone/something - couldn't have been my workmanship.
If the concrete was done properly salt has no effect what-so-ever.

Drilling holes with a heated slab sounds like a disaster waiting to happen. A Dave mentioned, they kind of frown on floor drains now and the floor has to be pitched towards the drain for them to work anyway.

Concrete shouldn't spall. It's often too much water in the mix. The excess water makes the concrete easier to work but weakens the surface.

Here is a link that might be useful: Portland Cement Association FAQ