I think it depends. When I practice my routine I will usually practice on a gymnastics floor (softer, more cushioned) until I'm closer to the show. Then I start doing one time per week on the hard wood aerobics floor.
As far as safety...the cushioned floor is better for the joints as far as pounding goes, but if you're like me and have "loose" ankle joints, it's a sprained ankle waiting to happen. The softness, for some reason, just makes it a lot easier to "roll" an ankle. I don't mind competing up on the harder stage. I don't think any of the ladies are doing such difficult gymnastics moves (like double twists and so on) that a softer floor would be necessary. But I do think that it does help to save the joints to practice on a softer floor (and for me, I practice barefoot and with my ankle(s) taped).
Hope this was clear. It is an intersesting question. But I don't know how they could make a stage more cushioned, unless they put wrestling mats or something up there. Personally, My worst fear is doing the routine after bodybuilders have been on stage.....oil can be very slippery.