Is Duet compatible with Mac OS X Yosemite (10.10)?

Yes!

Duet FireWire, Duet 2 and Duet for iPad/Mac are all fully compatible with Mac OS X Yosemite (10.10 to 10.10.5).

List of all Apogee products compatible with OS X 10.10 Yosemite

Please be sure to download and install the latest Yosemite compatible software package for your product from Apogee's site. Download Apogee Drivers & Software