On the Ubisoft forums for Rainbow Six Siege, community manager UbiEpi announced an update to their anti-cheat methods. While the wording is a little vague on how they are going to identify cheaters, once they have found one that person will be removed from the game immediately and be suspended from matchmaking for a period of time. You can read the full statement below.
In order to increase our efforts to counter cheating in Rainbow Six Siege, we will be expanding our criteria to identify potential cheaters. If identified as a potential cheater, that player will be immediately removed from the game and receive a temporary suspension.