I just tested it. It works, but I first didn't understand why. As the definition of \relax is copied to \definition, \definition is a TeX-primitive (right?). And \relax doesn't die in an edef (which I didn't know yet). When does the compiler kill the \relax then? Never at expansion, I would conclude. It is simply executed to nothing in the execution run, when an expansion run over the document didn't expand anything any more, right?
I'm not an expert like many others here. So I have to ask.