Install it without NEK. It will work with NEK for some time but you’ll get some nasty lockups if you try one of the Nek functions. Dongle calls are random, but are for real.
Nothing prevents you to install Nuendo trial and install the Nek feature later.
Before you ask, I tried to launch Nuendo 6 + Nek with the dongle of the Trial version and got the lockups.
Hint : Nuendo 6 trial makes a nice version to learn the feature at home on a notebook while the Big version’s dongle stay safely in the studio.