This needs more research. Most certainly the schools chartered under the Michigan Consititution (Wayne State, U of M and MSU) can create their own 'ordinances'. Other schools, I'm not so sure. They may have 'policies', but these generally apply only to employees and students, as their only recourse is dismissal or expulsion. Our local community college, KVCC (Kalamazoo Valley Community College) had an ordinance covering possession of a firearm adopted years ago by Texas Township. After pointing our the illegality and unenforceability of such an ordinance (oh yea, 30 emails, 9 months and 2 appearances at Township meetings), the ordinance was removed. They recognized that they did not have the statutory authority to enact, let alone enforce, such an ordinance.
So while the three Constitutional Universities are not covered under preemption, I'm much less clear that this holds true for all public universities and colleges. Private property rights enable any private property owner to control behavior on their private premises.
Carry on