Can you use fiberglass tape on things other than drywall?

I've used it with roof pitch to reinforce small repairs.

Use it for filler, backer, cut up for additional strength, in all sorts of unimportant things

probably not a grand idea ... it's designed to be embedded in joint compound, not to hold things together by its own glue and sinews

Yes. You can tape squirrels to cars. But not minivans.