I'd say going back to the crib cold be dangerous if he tries to climb out...although he isn't verbal, I'm sure he understands. My non-verbal 2 year old understood when I told him, "Mami has to sleep and do things in the house, so DON'T get out of the bed, or I will be very upset" He stayed in bed and cried, for many days, but he got the point..at the time it was the only thing I could think of, he's 9 now, and he still stays in bed even if he isn't "tired yet"
I'd say give the nanny technique a bit more time, but start earlier and make sure there is a routine. I used to tell him one hour before "In one hour it will be bed time" then as it got closer it was bath...read for 15 min, pray and lights out...he'd try to get me to interact, but I just left the night light on, and walked out.
So don't give up, whatever you do, he needs to sleep, and you have things to do, and need to rest as well..Good luck