@/allLOL FAQs Q: Scenery models have a Pitched Battle pro le. Does this mean I can include them in my army if I pay the points for them? A: No, the points are included for those instances when a spell or ability allows you to set up the scenery model, so that you will know how many reinforcement points it costs in a Pitched Battle.
(GHB 2017 FAQ v1.2)
So ... yeah ... that Nurgle player can't include Sylvaneth Wyldwoods in their army ... even with points.
“Nagash and Arkhan know all the spells from friendly death wizards, this means that they know the spell for Balewind Vortex If you have it in your inventory because your other friendly death wizards know it if you have it in your inventory.”