My Mavericks to El Capitan upgrade destroyed my hard drive and I only had very old backups, so I just re-installed El Capitan on a freshly formatted drive. I have managed to get ViewNX 2 working. It wasn't easy, and I can barely remember the steps, but it went something like this:
1) Purchase / install Pacifist
2) Use Pacifist to open the DMG archive. In my case it was S-VNX2__-021002MF-NSAEN-ALL___.dmg (148.8MB)
3) Extract Installers/Packages/EN/Contents of ViewNX 2.mpkg to the desktop as "Xtract"
4) Run "one" of the installers within the package. I can't remember which one I ran - sorry!. It fails complaining about not being able to write to "tmp". You will see that the following directories in Library/Application Support/Nikon have been created but are empty:
* Musics
* Profiles
* Uninstaller
4.5) Copy "Xtract/Applications/Nikon Software/ViewNX 2/ViewNX 2.app" to your Applications folder
5) Copy the contents of "Xtract/View NX2 Folder/View NX2 Folder/tmp/jp.co.nikon.installer.apppkg/*" to "Library/Application Support/Nikon/*"
6) You can now run ViewNX by running Applications/ViewNX 2.app but all the strings will be internal language placeholder strings
7) Copy "Contents of ViewNX 2_EN.pkg/Applications/Nikon Software/ViewNX 2/ViewNX 2.app/Contents/Resources/English.lproj" and "RegionConfig.xml" to "Library/Application Support/Nikon/Resources". This will get the strings corrected.
Apologies for the rambling, but I honestly don't remember quite what I did, but I just wanted to say that it CAN be done, on a fresh El Capitan installation, without a prior Mavericks installation. And probably in half as many steps as above. All I remember is trying a few things to install, it failed, I manually copied over the Library/Application Support/Nikon files from two places, and it's working for me. I hope my post gives someone some hope!