Mark Rein maintains that Microsoft prevented the developer from implementing clan support (e.g., Halo 2's Party System) into Gears of Wars' ranked multiplayer matches. But, in a recent interview with Gamer Andy, Epic's VP did hint that team support could still be added, stating vaguely, "In the future we might roll out some additional functionality."
In the meantime, a tedious workaround does exist. If one member hosts a ranked match, it's possible for the rest of the clan to grab spots in the match via the custom search menu. Of course, this method will become more difficult as the Gears player base grows and you and your teammates' TrueSkill ranks begin to differ.
Update: Gamer Andy contacted us to clarify that his conversation with Rein was not an interview. According to Gamer Andy, Rein's comments did not hint at future clan-play implementation. The cryptic statement about upgrading functionality was just an offhanded remark delivered to steer the conversation toward a new direction (i.e. away from concerns about Gears' multiplayer).
See also: Gears of War's ranked matches smell rank