Well only the sims you are playing will be able to go there as the rest will not use any of that - not the dive wells, not the Llama's, not the subways or hotair balloon, none of it. Fairies either fly or take a taxi everywhere - they mostly fly though - but any way, if they get the call to go to the Arboreum and can't get there they might act like stuck sims and complain about not being able to get there. I always place mine in the center of a lovely park or a flower garden in the woods along with some of the fairy castles and jellybean bushes. I'd make a path through the woods to that.
ETA - Also the school uses that as one of their field trips, so that may be a big problem. In fact the school uses that and the Vault of Antiquity as well for field trips quite a bit.
