If I were a thief, I'd be stealing things that would be easy to sell and fairly hard to tell that it was yours... I don't think a tire gate or a wheel with a 37" tire would be too high on that list. The tire gate is not all too common, and there's a way bigger market for a factory gate. Your wheel and tire kinda the same thing, the majority of trucks aren't going to be able to fit a 37, and if they do they really are only gonna want a full set.
I think you're putting too much thought into someone stealing it. I'd still lock them and all but that's it.