Fixed Spiderman Web of Fire 32X
It seems to be a 2-part problem, there was a bug in my alt priority scheme rendering, AND (this is what was confusing matters) the game writes an invalid priority setting with the 68k, which then gets picked up and used for the rest of the game.
It appears that the 68k does not have VDP authorization when it does this, and that write should be ignored. I'm assuming it's buggy code and ignoring it is correct behavior.
(and yes, you can play with spiderman on the Sega logo)