My first thought was the same as your first thought.
Ray Rice got married to make sure his wife can’t testify against him in his uppercut trial. The legal term is spousal privilege, but the BSO’s legal team has informed me that in the state of New Jersey spousal privilege does not apply if the crime was committed against your spouse.
As you can see from the video that is the case here.
That doesn’t mean Rice’s wife Janay Palmer will cooperating with police, but legally she can’t use the fact they are married not to testify.
The rumor is that the police don’t need her any way, because there is a clear video (different than one above) of what happened during the incident.