Im a Macbook user who has a Intel Core 2 Duo system, and currently use Mavericks as my main OS. I've been granted access to the Yosemite Public Beta, and after a couple of hours of testing on external HD this morning I can confirm that the current Mbox 2 10.3.3 drivers work the same way as they do on Mavericks (I'm currently on 10.9.2) with the use of a USB hub. I tested it with Logic, Safari Playback via Youtube, and iTunes. Everything worked as my current Mavericks setup does.
I can also say that I've had success with the Mbox 2 directly plugged into my USB ports of my Mid 2010 Macbook Pro, but that it was spotty very spotty. After installing the drivers and plugging it in and booting up Safari (only thing I was able to get sound out of) and testing a youtube clip the sound worked right away but made a few stutters before perfect playback, that could also be because I've booted the OS from USB.
Then I tried pulling the USB out and plugging it back in, and after the system recognized that the Mbox 2 was attached, it wouldn't continue playback of sound like it did when the system first started, but if I refreshed the webpage in Safari the playback would start again, but only after I refreshed the page.
As updates for OS X 10.10 Yosemite Public Beta come along I will continue to test these drivers out in the same capacity. I don't own current Protools software (10 & 11), so I can't test this or answer anything about that.
Just thought I would share my experience, and hope that when the final software is released this Fall that everything will work the way it should (As it currently stands). I'm someone who likes to be on the newest OS whenever possible, but if something works for you and you have full compatibility don't change anything.