You don't seem to understand how the cult works. The Ikuras cult differs from most spoopy roleplay groups in the fact that we always contact groups we intend on attacking and set up something mutually beneficial, an event that both groups will enjoy. Our summoning of Ikuras in the Druid Grove caused part of the grove to be corrupted, but it was arranged so that the new dedicants would have a chance to practice healing, and bring good publicity to both groups. The druids drove off the enemy, but Kknotos was brought back into the world.
Similarly, the Quandary event, in which Ouity was kidnapped, was done entirely by shooting Ouity a message to see if he was interested. We won't just attack random groups that have no interest in combating us. I passed this creature lore by Gigarun when he was in charge of the Druids and he loved it, going so far as to have the GMs broadcast the rhyme at the top of the lore across the server to all druids. It's a collaborative effort.
In regards to your Undead comparison, Fearwalkers are quite different. My group only recruits people we feel are capable, for one. Secondly, there really aren't any anti-druid groups that I can think of, specifically. I mean, there are general all-evil groups that target the druids on occasion, but there aren't any I can think of that go out of their way to become the druid's arch-foes.
And finally to answer your ring question - it's a spell, but the ring's wearer has to intend to turn that particular target into a Fearwalker when touching them. And of course, OOC consent is required, we don't want to force anyone to play a monster.
Well, that's the reason the Fearwalkers don't have a fear aura. The only fear element that comes to these creatures at all is their power to sense it, and if people don't wish to roleplay that, it's simply a lack of roleplay skills and likely won't inhibit the roleplay to too large of a degree. I doubt any players recruited to play these creatures will get in a fit over somebody refusing to roleplay fear.
Now onto the list of enemies that are anti-druidic. Out of those listed, I can't see any there that are specifically anti-druid. Two of those up there are server antagonists, and the Necromancer group and subgroups, as I remember, were on the whole dedicated to server-wide mischief, especially against clerics more than anything. And I've never seen a society of fire evocationists dedicated to attacking druids. So yes, I would consider this to be the anti-druid: this is the only group only dedicated to hunting druids and not much else, as other magics will kill them almost instantly with ease.
Regarding present-day Fearwalkers- no fear, the ones from the first generation are long dead. A new ring had to be forged, and a new group will have to be chosen to play these beings. This originates from the conflict with the Druids that the Ikuras Cult has traditionally had, including the kidnapping and poisoning of Ouity and the slaying of the Cult's Balrog by Elorna. For this reason they are very specified to druids.