I'm not even sure Assistant GMs count as "frontline personnel," though I suppose that is something the team would stipulate based on who they want to have access to the clubhouse and field.
But I seriously doubt Bonifay and Minnitti were among the the unvaxxed (or needed access to the major league clubhouse for that matter). I know the Phillies didn't mandate it, but they had the ability to put a lot more pressure on the non-playing, non-unionized staff.
Who do you think he voted for in the last two presidential elections?
There are small things that support my own guess, if you look. Trump and Q-adjacent stuff.
I also think the fact that he has never addressed vaccination - nor has the media been able to ask about it - suggests that he and the team don't want us to know. I hope he's not one of the ringleaders, but if he is vaccinated and was not able to change the tide in that dressing room what kind of leader is he really?