Would plates that are not marked "microwave safe" explode in a microwave oven or crack slowly?
Some might crack, but I suspect that there would have to be a significant moisture content in the material. I routinely nuke stuff on china, Corelware, Tupperware, and even some 45 year-old melmac plates that are already cracked half to death. There's never been a problem with any of them. There is, however, the possibility of toxic fumes and/or fluids being released.
They could also just burn your food or damage the microwave.
Test any plate by putting it empty in the MW on high for 10 seconds.
If it feels warm, don't use it.
Good idea. Also, don't use one with a pattern... particularly if it looks metallic.
Separate names with a comma.