Back pages are explicitly called out as allowed on the jam main page - it's properly one piece of paper, not one side.
Viewing post in Front side for players, back side for GM's?
Okay. What was tripping me up was the part of the FAQ which says, "The game can be spread across both sides, but keep the core rules onto a single side. Use the 'back page' for ancillary info such as GM tools."
The things I'm thinking of putting on the back are definitely "GM tools", not intended for the players and helpful for running the game, but they're not exactly "ancillary" either.
If it's fair game to put "player stuff" on one side and "GM stuff" on the other, then I'm good.