I don't think the Hunter commitment would have much to do with it simply because he's a NT in your scheme IIRC, while Garrett would be a DE, so I don't think they're connected.
I actually think the Hunter verbal is a part of it, but not because of scheme. I think it was just #'s and timing.
The coaching staff needed to come away with 4 DLineman this year, no matter what. When we were sitting at 2, and after Newman 3 lineman, we were willing to take pretty much anyone with an offer. And on paper, Goebel looked like ND's best chance at being an Irish offer (Catholic HS, Illinois product, visited the school on more than one occasion).
However, when Hunter verballed, it allowed ND to get more picky, and changed the name of the game. Getting a 5th DL commit might mean no 3rd DB, or no 5th LB, or might even suck away a scholarship from an offensive position. A.k.a, that 5th DLineman needs to be someone this staff sees as a "home run".
While the Irish went hard after Goebel, he still only got an offer by the 3rd week in April - about two months after OSU. He was the 9th of 9 DL offers, so its not like we know he was ND's top priority based on that. Coulda been admissions issues with his test scores, but it could just be that he wasn't the apple of Charlie & Co's eye. Who knows.
I think that Hunter committing when he did only made it that much easier of a decision for Charlie & Co. to put their eggs in baskets like Ethan Johnson's, and Kapron Lewis-Moore's. We already knew we were a bit behind with Goebel, so with the #'s game in mind it makes it a much easier decision to bow out. Either way, OSU (unless there is an unforeseen shocker at his visit to Ann Arbor) is getting a heck of a football player. He's a real smart player, who obviously knows leverage, and IMO can step in and play from day one.