Definitely G'raha is going to have valuable knowledge for Emet, one way or another, but that's still going to be true if he just knows how to drive the thing and not how to actually build it in the first place.
Ultimately his background is a historian rather than an engineer, which is why I'm hesitant to say "of course he knows how it works". He might understand the spellcraft side of things but be useless at the mechanical side.