I don't know if this will help. It was advice from Akai concerning compliant USB devices not showing up in OS X...I assume this would apply to any USB device, not just Akai products.
http://community.akaipro.com/akai_professional/topics/my-class-compliant-usb-device-is-not-being-recognized-on-my-mavericks-or-yosemite-operating-system-what-should-i-do-rcfql9dnfoaig
If your having trouble with class-compliant USB devices that are not recognized with OSX Mavericks/Yosemite, especially if it was working right before an OSX update, try the following: 1) Open Audio/MIDI Setup (in the Applications>Utilities folder) 2) From the top bar, select Window>Show MIDI Window 3) A listing of all recognized MIDI devices will appear.
4) Assuming your USB device is not listed here, click the Configuration drop down above and select New Configuration
5) Name your new configuration
6) Click OK and any connected but unlisted devices should reappear.
This particular symptom seems a bit more likely with class-compliant devices, but this would also be good troubleshooting for FireWire and USB devices with or without required drivers.
Hope this helps!