I just got a Virus TI and it works with Yosemite over here. I can report the following issues, but I can't be sure if it's specific to Yosemite, or just quirks of the TI itself:
- The USB connection seems finicky at times. I have it on it's own port with everything else on a hub. (surprisingly my Focusrite Scarlett 18i8 works just fine with a hub, but not so much the Virus) What I've noticed is that occasionally the USB MIDI stops working (get hung notes and inconsistent MIDI transmitted from the keyboard) Unplugging & re-plugging seems to fix it.
- Using the TI plugin adds latency to my sound card, which is on a completely different USB bus. When I enable the TI plugin, I get significant latency to the point where I can't play drums in real time on my Tempest or Electribe 2.
- I can't use the Virus as a sound card. When I enable the Virus as an audio device in Ableton, or aggregate it with my main sound card I get no audio from the Virus. The only way I can get audio from the Virus is by using the plugin. Therefore I am using analog outs on the Virus mainly. At the moment I reckon the plugin will be used for strictly patch management duties due to it's significant latency. (bummer, was really looking forward to this!)