I believe that it would still be considered a violation from the NCAA's standpoint if he participates in athletics. They recently changed the rule and I'm not all that familiar with it, so I could be wrong here, but I believe that because he signed an LOI, he must request a release because he still is in the initial 18 month window where other schools cannot contact a signed recruit. If he were to leave and enroll in school, his eligibility clock would start but he would not be able to use a redshirt year because he is prohibited from being on a different team than the one that he signed with. I will be one of the first to say that the NCAA has a bunch of outdated rules and I said that I think you are right that he shouldn't have to ask for a release in my post, but my original point said that the NCAA doesn't necessarily agree with us on what would be required to get out of an LOI.

It is similar (but also different) to the Wadsworth situation. He was the player who signed with Hawaii before his mission, but when he returned, he wanted to transfer to BYU. McMackin and Chow both wouldn't release him from his scholarship even though the time limit had past, so he enrolled at BYU anyway. The difference there is that he was outside the window that the LOI was signed and as of last season, he was still paying his own way for school if I am remembering the media reports correctly. (See Link for information)
http://www.cbssports.com/collegefootball/blog/eye-on-college-football/18828910/report-hawaii-releases-byubound-transfer-michael-wadsworth-to-anywhere-but-byu

As I mentioned though, I could be completely wrong in my understanding of the rules but regardless, it is pretty much a moot point. If the NCAA does require him to request a release, I think Bronco will grant it to him no questions asked. And if he is forced to sit out a year per NCAA rules, its already been pointed out that he most likely would be redshirting this year anyway, so that would take care of that part of it. And obviously, if Bronco didn't release him for some weird reason or if Wisconsin doesn't have a scholarship available for him, his dad has the money to pay for school either way. I just think that if the NCAA requires a release, he should follow the rules even if I don't agree with or understand their reasons for it.