I generally don't use any thread locker on the pump (or IO) bolts of any boat or watercraft. They are already hard to get apart after sitting in the water. I coat them all in anti-seize.
If the bucket is up, and out of the jet nozzle... there's really no worry about it dropping into reverse. The reason is... and a lot of people don't realize this... but it's completely out of the water when on plane. Heck... your entire pump and nozzle are also out of the water when going. Only part of the system in the water is the intake grate. Because of this... there's nothing pushing it back down.