Yes. I've allowed access to Photoshop for the guest account. I can open Photoshop, and when I do an import->twain select, i can't see the scanner there, so I can't scan. However, in the Owner/Administrator account, I'm able to see the scanner and thus scan.
I think I've also allowed access to the required extension & preferences. What are the required extensions and preferences by the way, just to double check.