[robotsteve2]

Their observations of nature and their ability to predict stuff should be consistent with ours.

They might not use the same mathematical tools or the same physical models, but they should make the same predictions. That is, we might not be able to understand their theory of gravity, but whatever their theory is, it has to be able to make predictions about orbits, black holes, etc.

I don't think we could assume much about the mathematical concepts they use beyond that.