I've been in gyms where there were serious power lifters. They all used belts on the deadlift, the heavy, multi-layer-leather stitched kind. Google "powerlifting deadlift" in the images section.I never used a belt or gloves when deadlifting. But chalk is a must just for grip after a certain range. I'm a small dude. 5'9 175-180 ish, and I can hit 405x5 raw, no chalk, with chalk, I can probably add another plate easily.
Belts are typically seen as bad because they cause destabilization of core muscles. Think of it in this plane, Real lifters don't fukk with machines, because it controls the equilibrium.
edit: Basically without going into a bunch of jargon, using a preventive belt, can cause more harm down the line, than not using a belt...
Good form should be your goal.
They also used machines, if you want to believe that or not.
There is this weird machine called a reverse hyper, created by a power lifter for use by power lifters. I used it at this one gym that had serious power lifters. I used it sometimes. Power lifters would use machines sometimes, but in a capacity where they aren't going for one-rep max.