No lawyer is going to tell you to go ahead and OC. If you get jacked up for some bogus charge then you can go after them for poor advice. Lawyers are always going to error on the side of caution.
Some MAY be willing to tell you it appears that OC is legal... but then again, they DO tend to ERR on the side of caution...
Seriously though, everything Venator said is true. In addition to what he said, what you will find is that most attorneys only know that part of the law which they tend to have considerable experience; remember, the whole notion of OC is relatively new (in Michigan). Most firearm violations that the courts and attorneys see are either "felon possessing a firearm" or "concealed carry" by unlicensed individuals. I have researched as much as I can and it just seems that most firearm legal issues get dealt with very early in the legal process; this is for both the aforementioned violations and OC. That being the case, most attorney's have a very meager understanding of the intricacies of the issues involved due to not having to really deal with OC regularly.
I am not trying to absolve attorneys of their responsibility, though. But, like most people, they tend to do that which is "easiest"... and in the case of OC, it is "easiest" to list all of the worst-case scenarios one could face.
BTW, in reply to your question regarding the AG opinion you mentioned, it would probably be helpful for you to know that "Reserve officers" DO NOT have general arrest authority in Michigan. In fact, they have no more inherent right to carry openly in a PFZ than you do. However, it is interesting that, since this opinion was promulgated, Reserve Officers have been added to the list of those "special" people who are exempt from the cc in a PFZ prohibition. As a person who was a reserve deputy in MI, I can honestly say that they have very little training (dependent on department) and the thought that they are somehow possessed of some special skill-set that should exempt them from the cc in PFZ prohibition, yet stops a general citizen w/ a cpl from doing likewise, is simply ludicrous.
