In VP, go to Options/Preferences and select the VST Effects tab, then use one of the Alternate VST Search Folders to Browse for the VST folder in which the Nectar 2 and 3 .vst files are held under C:\Program Files or C:\Program Files (x86). You may then need to hit the Refresh button.
I have Ozone and RX adv, and a few other plugs installed. No problems here with iZ plug-ins in VP-16. ( (or VP-9 for that matter), Some ASIO devices are known to cause problems with VSTs though, especially when used on the master buses.