G’day Ben
At least you are backing yourself and trying something. At the end of the day evaluate and make your own decisions and the real odds are that you will be better for the experience one way or the other.
But for my 2 cents, I believe it is a big leap of faith that any TA activation exercises will transfer to any of your Rugby skills. I also believe it is a big assumption that your players won’t be able to recruit TA unless they have some back pain which may be causing inhibition. Even if you were trying to activate TA, it is an extremely hard thing to do consciously (it should just occur naturally) unless under ultrasound so most players will just end up bracing through their abdominal region. Not that bracing is a bad thing. So in a group environment I think it will be difficult to achieve what you are trying to do. I believe just doing your wrestling drills will force your players to brace through their abs like they are about to take a punch which is what you want. Some general ab and bracing exercises are fine and i particularly like things like plate walk and chops or walking plate rotations etc. Remember that all S&C is general and a means to an end so you must use your time wisely to get as much bang for buck out of each activity as possible.
Hope my ramblings make some sense!
Cheers
Damian