Actually, game-chat would probably be a good (for them) way to hide certain types of planning. I'm not saying it's true, but for a modern shooter or perhaps FPS, they could simply substitute "game" targets for real-life ones, and otherwise the conversation might sound much you would hear in some games.
OK, so sneak your infiltrator into the enemy Science Centre. There will be about 3 guards in positions X, Y, and Z. Group B will take them out, then you delivery the package by 14:00. Meanwhile group C enter the mass relay by 13:50, and take out all present. Group A will attempt to take out enemy power infrastructure and cause confusion at 13:30.
Maybe some of it would sound like weird BS, but would *you* suspect that some of the weird guys in CoD were actually plotting nefarious things in real life? Some of the shit that trolls said might be a good cover too, as most sane people either mute them or just ignore it. As a mid-level gamer I'm not sure I could tell the difference between a real-life nutball and the online nutball variety.