Dress code contracts typically include language to the effect that those who do not abide by the dress code (conditions of the contract) will be required to depart the premises. Their failure to depart, when requested to do so, becomes trespassing ... and can quickly escalate to disorderly conduct or assault. These most certainly are criminal matters. The cop was "moonlighting" as a private security guard, thus was well within his authority to :
1) request that the guest abide by the terms of the contract that allowed him to be on the premises
2) arrest the guests who became disorderly rather than abiding by the contract.
This simply is NOT a matter of police or state overreaching. It's a matter of a young punk acting like a young punk, and two old idiots who should know better aiding and abetting him. The groom has no excuse whatsoever: he signed the contract, he knew its contents.