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.