I'm in the middle of the same nightmare. But I learned today via Mark Wallace's demo for Tethering Tools that indeed Adobe Lightroom CC and Apple's El Capitan are not on speaking terms at the moment. I am given to understand, however, that Adobe's engineers and Apple's engineers are trying to work this out. Your guess is as good as mine as to when and/or if this will be resolved. Had I any idea that this would happen, I certainly would have not updated to El Capitan until the issue got squared away. Alas, I didn't know what I didn't know. So, kellyp40462520, I guess we'll just have to wait it out. Meantime, I'm back to swapping memory cards from camera to card reader and back. Aggravating, to be sure. Tethering indeed does tend to spoil a dude. Should I hear any good news, I'll check back here to share. At least I know now that my gear is not at fault; I was beginning to worry about that prospect.
P. S. I neglected to mention that, apparently, this issue pertains to Nikon(that's me) and Leica cameras, and possibly others, although I believe that Canon's relationship with LR and EC remains solid, which, I gotta say, hurts my feelings!
Adobe just today(01/27/16) released a LR update 6.4 and it now tethering works with Nikon. I just tried it and it now recognizes my D810. Perhaps the nightmare is over!