If they are fabric belts, I would not suggest a liquid sanitizing spray.
a) you are wetting a fabric belt
b) you are sanitizing a surface that is not "clean"
This really all depends on your process. I have fabric belts and really do not do anything to clean them. The baking process is considered a kill step. Is this the best solution? Probably not, but outside of changing all belts to a material that can be wet cleaned and sanitized, you don't have too many options.
And even with that, you open yourself to many other issues that go with wet cleaning.
Marshall