Can Corian sheets be used in a steam shower?
Most likely, you'd have to check with the manufacturer, though I'm not sure you really want to be heating up "plastic" like that and breathing the fumes. Granted, we're not talking about searing heat, however, it doesn't take much to get plastic and resin products to emit toxic off gassing.
The brand you mentioned has never been on my list of preferred materials for showers.
Tile would be better for a steam shower.