I don't know what the rules are now, but when I was active in the Hurricane Club some years ago, I had occasion to learn the rules, and back then, anybody who represented the school's interests, as I think the rule put it, could be restricted from contact. This would encompass not only boosters, but alumni. Barrow is an alumnus, so if the rules read the same way they did back then (late 1980's), then there would be restrictions.
Unless the rules have changed from that time--and that was around the time the NCAA started drafting some comprehensive rules covering boosters, alumni, etc.--there would be restrictions.
Back in the very early '80's, and before, it was wide open. I have friends who were active in the Hurricane Club back then, and some of my friends were asked to write letters to recruits. I think a friend of mine wrote to Bernie Kosar when he was still in HS. My friend used to go to breakfasts with recruits. I don't think that happens the same way today. I met another UM alum from the Pittsburgh era, who used to officiate a lot of high school football games, so he knew the football scene in that area. I remember him saying how one of the coaches called him, and this was back in the '70's, and asked him to call a couple of recruits in the Pittsburgh area. One I think, was Jimbo Covert, who became a great player at Pitt, and another whose name I can't recall, went to Clemson.
I suspect Mike Barrow is going to pretty much keep out of the scene now. i would normally say he's really gone for good--and I have no way of knowing what his situation is--but we've had a number of people who have left and perhaps didn't have the greatest relationship with the then current coaching staff, somehow ended up back at the U. Two were Don Soldinger and Art Kehoe. I didn't think Kehoe would ever be back after suing the university. I'm not saying that's true with Barrow. With all of these guys, the family ties and the U experience overcome more transient things.
EDIT: After looking a bit at the NCAA rules, I don't see any restriction on "alumni." That might have been removed some years ago. I notice they revised some of the rules in 2000, so they might have loosened it up for alumni. He might still be considered a "representative of the university's athletics interests" as that term is used in the NCAA recruiting rules:
Representative of Athletics Interests.
Previous Cite: 13.02.13.1 Recruited Prospective Student-Athlete. Next Cite: 13.02.14.1 Duration of Status.
A "representative of the institution's athletics interests" is an individual, independent agency, corporate entity (e.g., apparel or equipment manufacturer) or other organization who is known (or who should have been known) by a member of the institution's executive or athletics administration to: (Revised: 2/16/00)
(a) Have participated in or to be a member of an agency or organization promoting the institution's intercollegiate athletics program;
(b) Have made financial contributions to the athletics department or to an athletics booster organization of that institution;
(c) Be assisting or to have been requested (by the athletics department staff) to assist in the recruitment of prospective student-athletes;
(d) Be assisting or to have assisted in providing benefits to enrolled student-athletes or their families; or
(e) Have been involved otherwise in promoting the institution's athletics program.
The next paragraph, which I have not reproduced here, states that an individual retains the status indefinitely. Barrow might be considered to come under this definition, and hence, will be restricted. I don't expect him to get involved in recruiting.