Is Duet 2 (USB) compatible with Pro Tools?

Yes!

Duet 2 appears as a Core Audio device on your Mac and is compatible with all versions of Pro Tools, starting with version 9 and up to the current version.

Duet 2 is not compatible with any version of Pro Tools 8 and lower, or Pro Tools LE.

See "Setting up Duet 2 (USB) with Avid Pro Tools" for more info