Blight druids should be non-app though, and set kit. They just dont need to be OTT stats wise.
When i say taint, it could mean desecrate. Malarites/orcs desecrating Seladrine, etc.
I would not support that unless there was a way for the grove to defend itself. Otherwise randos can wander in and taint it for teh lulz.
The idea is only a druid can claim a grove. So in theory a druid could take over a grove and taint it. Otherwise, they would have to be invited by the druid who claimed it.
My only concern is that if you have multiple groves, they should really be focused. The grove we had was great for your Silvanus/Chauntea types. I think a grove in the deep forests, essentially a shrine to the Seladrine would be good and work well as a faction base for elves. I think there should be a natural evil aligned grove too, perhaps in a swamp area which could double up as a barbarian/malar/talona base. Tainting/cleansing groves of rivals and especially the Seladrine are core to a lot of concepts.