I know that it has not yet been determined yet which cap he will be wearing on the plaque, and I would love to see him go in as a Mariner, I actually think they will go with the Diamondbacks because of what he accomplished here. I am actually pretty excited to see him go in as the first Diamondback in to the Hall of Fame and leave Griffey to be the first Mariner to go in to the Hall next year (hopefully followed by Edgar Martinez).
I really hope he goes in with a Diamondbacks cap! I know it's not all in his control, but his most dominating years were here in Arizona. Hadn't thought about the Griffey aspect, but that makes sense.