How does this application using the Dust Deputy work with using the Festool Sheetrock sander Will it collect Sheetrock mud dust as good as it collects sawdust??

The Ultimate Dust Deputy can definitely be used in combination with the Festool Planex Drywall Sander. Customers have reported exceptional dust collection when using it, significantly reducing the amount of dust in the vac bag. You can find some first-hand reviews on the Festool Owners Group forum if you'd like to additional feedback.