Just a quick heads-up that the EyeTribe server is having very similar problems under El Capitan / 10.11 developer previews for us as it did with early versions of Yosemite. Basically it will sometimes connect, sometimes be 'seen' but not initialized, and other times just confused with the built-in iSight or other cameras on the machine.
Note, however, that there are a whole mess of USB issues we've seen with the 10.11 DPs that range from audio output, measurement device input, and others. We've reported everything we've found to Radar @ Apple and it appears by the bug coverage that they are aware of and fixing this stuff.
So- if you want your tracker to keep working, don't upgrade to El Capitan yet if you can resist
