I don’t think it’s specified one way or the other if the removed treasure is revealed, but because the “more than half” rule isn’t used, there’s no real need to reveal it. Unless something else forces it, or the group/person running the event decides otherwise, it’s safe to assume it does not get revealed.
In that case, I assume that treasure eliminated via an Isle of Fire would have to be revealed in a 1v1 standard game?
I would think it still doesn’t get revealed, because since abilities that add to the original 30 gold don’t change the requirements of the more than half rule (16 gold), it seems like subtractions from the total amount of starting gold would also not affect the required total of 16+. Eliminating treasure just makes that endgame condition less likely (or impossible if a lot of coins are eliminated), so the game is more likely to end with all treasure unloaded to HI’s or no future move actions.