Your scenario has nothing to do with the 30/120. If the person is entitled to the work, due to seniority, then management can't stop him. This is the attitude of some of the younger guys. They think if they file because they are wronged, then they will get on managements bad side and will be denied work.
As far as contract being poorly written, I agree. This is all written in lawyer speak and at times can be hard to understand. That's ridiculous and is counter to being what a contract should be.
If management is DQing people, they need to be doing something to be DQd. It may seem as simple as MGMT not liking them, and in some cases this may be true. However, I would get a BA involved with that.