Since the DOH says wearing a mouthguard and mask may be hazardous and it is, therefore, an exception to wearing a mask, and it appears there aren't any feasible alternatives, if a hockey player believes they have an exception under Section 3 of the order, they may play without a mask if necessary.
Let me know if this resolves the concerns, or if you have any questions.
David D. Donnellan
Mt. Lebanon Recreation Department
900 Cedar Boulevard - 2nd Floor
Pittsburgh, PA 15228
Phone: (412) 343-4519