To OP, your best bet is to go over to the Tascam forums and ask about experiences with Yosemite.
http://www.tascamforums.com
I know the driver signing in Sierra messed with some of the Tascam legacy drivers but again, I would ask on a Tascam forum.
Also, seeing as Tascam.com has drivers for Mavericks, Yosemite and El Capitan, again, you should be fine with Pro Tools 11, the Tascam drivers would of been my concern.
http://tascam.com/product/us-2000/downloads/