You were right!
The gacholoth has "immunity to charms" listed in its SQ line.
The dharculus has the following:
Immunities (Ex): A dharculus is immune to all mind-influencing effects (including charms, compulsions, phantasms, and morale effects.).
The nic'Epona has this:
Immunity to Charms (Ex): Nic’Epona are completely immune to all sorts of magical charm spells and effects, as well as any sort of magic designed to gain their trust or coerce them into doing something.
I think what the nic'Epona has is what we're looking for.