Since it says not to flat tow, I would NOT do any engine off coasting.
Yes, even in neutral the torque converter and oil pump will still pump enough fluid. I don't know the exact details of your truck, but in general in the vast majority of vehicles it is fine. The torque converter is attached to the flywheel of the engine, and spins with the motor, so even in neutral it will still pump enough fluid to keep the trans lubricated.
A little while back my old Neon (automatic trans) was having some problems and had to tow it a short distance home, but wasn't worth a tow truck, so we just flat towed it. It wasn't very far, and we were just towing at slow speeds, but what I did was put it in neutral and ran the motor to keep from hurting the transmission. It burned fuel that way but I figured it was worth it to save me any more for repairs.