I think you'll get different answers from different people and their experiences from crossing the border. I believe it all boils down to what a particular customs officers is in the mood for when you happen to cross...lol. If I were the OP, I would honestly wait till his spouse's passport is in her hand because it is definitely better to be safe than sorry.
I do however, have a word of caution for the OP who is the USC- I hope that you yourself have
your passport as well! When my husband (the USC) and I (the CPR) crossed the Canadian/American land border crossing at the beginning of July, coming thru American customs on the way back, I handed him my and my daughter's green cards and my hubby handed him his Virginia driver's license...what he has ALWAYS done for many previous years and it was accepted. The officer looked at our green cards then at me and my daughter's faces, smiled and gave me back the cards and then said to my husband "Yeah, I have a driver's license too - do you have your passport?"

Luckily, we had ALL our passports with us but I just thought it was SO funny that it wasn't ME who had a hard time but my USC hubby!
So have
your passport as well as your wife's at the ready, ok?