I do not need the tug pilots "Ok" to box the wake. Although as a courtesy in a training environment I will call to ask him to "hold heading" for the student. It's normally been pre briefed before takeoff anyway.
Boxing in a turn, no issues, it's a little tough for the tow pilot when you are inside the turn, he has to work harder, but he'll be rewarded when you are outside the turn.

As a CFIG and Tow Pilot, we train our tow pilots. It's hard to get qualified Pawnee tow pilots, so we grow our own.
During qualification training I will go to the left and right limits on tow so the new tuggie will know what could happen. I will not go to low limit, just a little lower than a normal box the wake. I will move off to the side so I can see the tow and move to a god awful high position so the new tuggie can realize what could happen if a glider kited on him.

I had a visiting glider pilot that zoomed and turned to "spring board" off the tow to get some extra altitude. I saw him go low and felt him start his zoom climb. He yanked me pretty hard and was late on his release and pulled my tail up and side ways, I told him if he tries that again it was his last tow at our club.
BillT