Call of Duty 4's AI can't even be considered dumb becaue that would imply that it would have some measure of intelligence, however small.
All there really is to it is spawn, move to cover point, and fire (or not fire in the case of your allies.) Sometimes you'll get some scripted moment that, for a moment, breaks up the retched monotony but that does little to compensate for the terrifyingly shallow gameplay that saturates every nook and cranny of that game like warm, month old butter on a carbonized muffin.