Surely the reason that a class would require factory ammo only is a libility situation. Two angles, perhaps. 1) someone brings monster hot double loaded magnums or whatever, gun blows up, injures kills someone etc... 2) untrained student turns with bad muzzle discipline and shoots another student. We all know those evil handloaded booletz kill people with more evil intent than those more friendly factory loads. That's what the other guy's atty will try and present.
The reason that LE agencies would require duty ammo for training is so that the cop gets used to shooting his duty ammo. This one makes more sense than the other one. If you're going to shoot in the line of duty, you surely want that bullet to go exactly where you think it's going to go. That same "other lawyer" will have a field day with "You trained on this other ammo then you shot my client with this here ammo?".
To address the question, I don't train formally. So I don't "require" any particular kind of ammo. You bring some guns and ammo, we'll go shoot. I'll coach you ONLY if you ask. I have several students, but it's all very informal and one on one.
Sgt Lumpy - n0eq