I don't see how the collar or ears are a big deal. I can see the tail being a potential safety issue, both for the wearer and for others. Multiple aspects of operational safety rely on the assumption that the human to be protected has not tied an easily snagged 3-foot cloth appendage to one of the few parts of their body they can not see under almost any circumstance.
And I can see how the park may object to a guest coming in looking like an arbitrary costumed character. Kids and slower adults will be confused.
What I just can't see, even as a completely nonreligious person, is any reasonable individual claiming equal status with Catholicism at an amusement park simply because s/he wears an ASTM-F24-noncompliant costume everyday and finds special personal meaning in doing so. By that standard, my diet soda habit is a spiritual experience entitling me to special exemption from the food and drink rules at every TSA checkpoint.