Tried killing some Field of Bone Iksar guards with a lvl 50 shaman and a lvl 50 bard. Everyone we tried was white con at 50 and had 100% MR. Must've cast "root" at least 30 times, "malo" a whole bunch, and bard couldn't land a single song either over the course of about 45 minutes of trying.
Proof that you could land spells on these guys:
http://eqbeastiary.allakhazam.com/search.shtml?id=4217
necro giving a battle report on how he killed a guard, mentions spells landing
http://eqbeastiary.allakhazam.com/search.shtml?id=7951
another battle report from a different necro, mentions spells landing