Well, let's think about this logically.
All people who are not evil cannot be zombies.
However, evil in the more "earthly" sense is a point of view; so what we must first determine is whether or not his point of view conflicts with those of the greater RMXP society.
Since a person's point of view is largely determined by their circumstances and past experiences, we can deduce that PoV = experience + circumstances.
Now, experience is something which is gained through a person's trials and hardships in life... and trials require you to go to court. So logically, if a person has taken part in the judicial system, they must be experienced.
Circumstances are made up of the events that surround a person's birth and environment. Since the environment is a fickle thing that is easily disturbed, we must all be very careful to properly dispose of our C-cell batteries. Clearly, this means that the average individual who cares about the environment should be very familiar with C-Cell batteries.
Therefore, his point of view is determined primarily by the length of time he's spent with the judicial system and his level of expertise regarding the proper disposal of batteries.
A person who very frequently goes through batteries is almost certainly experienced with disposing of them, so he's probably of an occupation that makes use of a device that requires multitudes of them... such as a flashlight. And what job requires a flashlight and is intricately tied to the court judicial system? Why, a bailiff, of course.
And since we know that all bailiffs in zombie movies die, and therefore become zombies themselves, they must also be evil.
So... if we can prove that Getsuga was employed as a bailiff at some point in his life... we can prove beyond any reasonable doubt that he must be a zombie.
Also, I like pie.