Serebii's page says that if you show a lady any of the 3 Pokemon, you get it. Does that mean you can use them on any of the three Incarnate forms, regardless if they are DW or not?
Link to serebii
Yes you can.
This video is a walk through on obtaining the Reveal Glass in Pokémon X and Y. In the video the player narrating has a Landorus with it's Hidden Ability Sheer Force, a Thundurus with it's Normal Ability Prankstar and a Tornadus also with it's Normal Ability Prankstar.
After he get's the Reveal Glass from the lady in Reflection Cave, he is able to change all three Pokémon to their Therian Forms and back again to their Incarnate Forms using the Reveal Glass despite only one of them having their Hidden Abilities.
Additional Sources: http://bulbapedia.bulbagarden.net/wiki/Thundurus_(Pokémon)
http://bulbapedia.bulbagarden.net/wiki/Tornadus_(Pokémon)
http://bulbapedia.bulbagarden.net/wiki/Landorus_(Pokémon)
Hope I helped :)
