One of my co-workers had a long-running review open, and ended up rebasing his local changes several times (on top of remote changes performed by others in the stream). This caused unrelated changes...
We have the same issue with GitHub. Merge commits pollute the reviews and Rebasing breaks Collaborator.
I worked with the dev team to try to exclude merge changes, but it gets tricky when there are conflicts.
Not sure how UCM works but for GitHub it'd make more sense to show a diff of the dev branch vs. latest master rather than keeping track of incremental commits on the dev branch. That's what GitHub pull request diff does.