Not necessarily. Congress's power over military installations is covered by the 17th clause of Art. 1, Sec. 8 which reads "...to exercise like authority over all places purchased by the consent of the legislature of the state in which the same shall be." As Federally "owned" property Congress can stipulate conditions for accessing or using it.
This clause would not cover the law in question since the law applies both on and off military installations. Again, without a tenuous argument tied to the "necessary and proper" clause I fail to see how Congress is empowered to enact these restrictions.
I am curious to know what you think are the limitations to Congress's power under the "regulation of the land and naval forces" clause. If Congress can prohibit the wearing of unearned medals by civilians not on a military installation, can they also prohibit the wearing of an Army PT shirt or uniform-like clothing? Stipulate a national diet for teenagers to decrease training time for new recruits? Prohibit "boot camp" style fitness programs for civilians?
Thank you for proving my point!
Ribbons are property of the U.S. Armed Forces and Congress can stipulate conditions for using them!