There is no such thing as a zero TID (as far as I know). Admin introduced the zero for PID specifically so that cards that were getting PIDs but shouldn't could be forced not to. Then it also became the standard to use for a card that just shouldn't have a PID (such as checklists) so that when doing Name validation, there would be no red spots.
As far as the GPKs and PIDs, I would say they can have them since we give other fictional characters PIDs, but they need to be marked as fictional non-human.
-- Dan --
Note: Please see my profile for more info regarding trading (section updated 3/4/2024). I have added a large portion of my inventory to the site, and currently have trading turned on (details are in my profile).