I'm no pro, just a DIYer that likes to paint ;)

"I have two painters, both with excellent reputations who seem fanatical about priming..." That's a good thing!!

"It's certainly possible an oil-priming might be necessary for these windows, but I've heard that oil-based paint can trap moisture underneath and cause bubbling." hmm, I've not heard that one. The oils in the primer will absorb into the wood, not sit on top of it (bare wood, anyway). Are they taking it down to bare wood (sanding peeling flaking paint off?) Can only give you my .02. Our house was painted cedar siding when we bought it, wood trim around windows/doors. For windows and doors I used Zinsser Bullseye 1-2-3 (a latex primer) and then latex paint over that. It held up quite well till we eventually put up vinyl siding (about 7 years after painting). Just my humble opinion, but would think quality of paint is what's going to get you longevity. When it comes to paint, it's often very true that you get what you pay for.

I wouldn't be adverse to letting a painter use an oil-based primer and a good quality latex top coat over that. There are so many high end latex products available on the market these days. I personally would not want an oil-based topcoat simply because of the yellowing factor. Oil-based paints, especially lighter colors (white, cream) are notorious for yellowing over time (I used oil-based top coat on our interior doors when we first bought our home. It was a deep cream. We've replaced most of the doors, but still have a couple more to go. On the remaining doors, that deep cream has now aged and yellowed to a medium yellow beige. Not attractive.)