"He’s a great stick n rudder instructor but has never flown aerobatics himself. My thinking is that while he’s not going to teach me, he’ll be my backup, having a good chance at fixing something if I get myself in trouble."
In my strong opinion, there is NOT a good chance a CFI who has never flown aerobatics will get you out of trouble during a botched maneuver. This requires the ability to both anticipate and see in real time errors that new pilots make with difference kinds of maneuvers, and to intervene with the proper inputs before things become dangerous. This takes experience. The non-aerobatic CFI is essentially dead weight up there. Either you are good to practice the basics on your own, or more practice with an aerobatic instructor is needed. This video shows very basic positive G stuff. I don't see any red flags in the pilot's performance.