If its demonstrated that the deceased wants a particular symbol on their grave that is based on their beleif system, I really don't see the big deal. He was Wicca, ok, give him whatever they use, cripes the guy died in the line of duty.
I can just see the waste of money on a "Office of Recognized Spiritualism" that spends its time and money deciding what religions are "accepted" or not, with a budget of 100 million per year...and files, we have to have lots of files.
Give him the freaking headstone and be done with it.