Yes. It's perfectly fine, and the heat is not a problem at all for decks made from composite materials.
There is zero concern for using snow melting mats on composite decks! You don’t need to use a thin layer of plywood or carpeting underneath your heated snow melting mats. You don't need anything underneath the composite decking because the heat is not going to affect it.
However, we recommend that you don’t put snow melting mats on brand new composite decking. If it's a brand new composite decking, you should let it fade for a few months and then put the HeatTrak mats out. Otherwise, our mats (or any mats, for that matter) will block the sun and your deck won’t fade evenly.