Rainbow Six is Halaal:

The first category is games which help in jihaad for the sake of Allaah, whether that is physical jihaad (fighting) or verbal jihaad (i.e., knowledge), such as swimming, shooting, horse-riding, and games which involve developing one’s abilities and Islamic knowledge, etc. These games are mustahabb and the one who engages in them will be rewarded so long as his intention is good and he seeks to support the religion thereby. The Prophet (peace and blessings of Allaah be upon him) said: “Shoot, O Bani Adnaan, for your father was an archer.” Shooting or archery includes by analogy all similar actions.

The second category is games which do not help in jihaad. Example: games which are specifically forbidden in the texts, such as playing with dice as mentioned in the question. These games should be avoided by the Muslim.