Seems like it would be easy to test. See how the AI does when revealed pieces stay revealed compared to a standard game.

Also, given this is online competitive play likely that a significant portion of top human players are cheating and have aides to keep track of pieces.

Most good players of stratego have perfect memory of all revealed information during a game. That's basic table stakes for playing, like memorizing the dictionary is for scrabble or memorizing openings for chess. It isn't very hard to do, since most moves don't reveal the value of piece and those moves to do reveal a piece tend to led to the destruction of that piece within a move or two. A computer isn't going to have an advantage there.

Yes, playing it as a kid I remember one pretty common thing to do was to make movements that made it easy for your opponent to get confused about whether a piece was that known piece or something else. Not the whole strategy but take that piece out and you definitely change the game I would think relative to typical human play. Especially in the context of it normally being more of a kids game.