I notice the last addressing of this issue was in February of this year. I have hesitated to upgrade to El Capitan for almost a year now. While I have been a Nikon Shooter for longer than I care to admit to, I'm continually disappointed in Nikon's reluctance to get with the program and I'm sure they are once again the source of this problem.
The question is... Has the problem been solved? Can I now confidently install the latest MAC OS and shoot tethered to LR with a NIKON?
Yes, the El Capitan upgrade broke the tethering of Nikon and other cameras.
Nikon fixed their SDK.
Adobe built a new version of Lightroom with the new Nikon SDK.
Lots of folks say Nikon tethering now works again in Lightroom. I am a Windows user, so I cannot verify any claims about the fix (or the problem).
Yeah this was solved quite a while ago.