There's at least a dialogue option that implies you can, but I'm not sure if it works out for you or not.
Tip: When you get to the grove, sneak into Kagha's personal storage chest and read a note in there.
back in EA there was an option that you could say to the shadow druids that you wanted to join. You got denied simply because (as per lore) you did just the oposit of what needs to be done. The only way I can see them letting you join is to
1: Open that chest and read the notes
2: Go to the swamp and get the additional info
3: Let Kahga finish the ritual and shut the grove off anyway (I think you would need to kill off the Tieflings and possibly kill off Halsin and kill off/ignore the gobos).
THEN later in the game, a Shadow Druid representative would approach you at camp and explain to you the whole store and invite you into their circle (because you did not reveal their plans and let it happen). As a druid you can chose to join them or turn them down. Mind you lore wise if you turn them down, you are now a liability and will be eliminated if possible. This would set up a nice ambush with them later own.
I may have to just bite the bullet and try the above and just see what happens. The developers actually added that conversation about not getting an invitation to join them (the shadow druids) during the confrontation in the grove after I brought this up the first year of EA (the lore behind it). Maybe they added the rest of what I said... dunno, I am not taking credit for it, but it was an interesting coincidence. They have a policy of not responding here often, but they do read pretty much everything we post...
