yes, OCTGN by itself is not a secure way to play games. Even something as simple as modifying the game's python scripts can open up opportunities to cheating. This cannot be controlled with OCTGN's current implementation, as quite a bit of the game states are stored locally on the player's clients. There are future plans to address the "security" of games, which had originally been part of the subscription funding campaign
OCTGN is basically for playtests. Cheating would be a stupid way to playtest.