I watched it again, and I am pretty sure that the finale is totally a dream. It has to be. There are so many truly unbelievable things that went on in this episode--one right after another. It seems that everything stems from from Beckett's insecurities and fears of ALL that could go wrong. If looked at with that premise in mind, the whole episode is pretty hilarious.
Making Kate stupid and weak has to be fake. She 'didn't know the marriage was legal' is too far fetched, since her parents were lawyers and she herself was pre-law. Not to mention the IRS would have noticed her single filing status. And the AG office would have totally done a background check and would have wanted to investigate her husband. She gives all the power to Rogan, and does anything he wants when he won't sign the papers, even breaking into a car! That would never happen for reals. Tough Kate Beckett would tell him to do it and he would!
Particularly amusing was the demise of the ugly dress. Lanie said a 'pipe broke' at Kate's apartment. They only show the dress for a moment, but it seems to be a SEWER pipe that broke all over the dress, because it looks way darker than just water.
Everything that happened is too far-fetched, ridiculous, and basically not believable to be real. It has to be a dream!