It depends on the composition of the salt. The 'common' salt is sodium chloride. That is a no-no. It degranulates the shingles. You can use calcium chloride.

If he uses calcium chloride as stated above he should still rake the bulk of the snow off. If this person gets the snow melting the water will run down to the ice dam causing more of a dam and/or more leaks. Like I said before I would rake the snow off and then wait for a sunny and warm day if you have those and then get to work on the bottom of the ice dam first, working your way up. That way the water will be able to go down. What about buying some roof cable to heat the ice?

Good luck,
Devildog