We had a group that did a great job of merging between branches. As a developer i appreciated all the work it saved me and would recommend this approach highly if you can find the right people to do it.

As the group contracts though it seems developers will have to perform the merges. Developers as mergers encourages a flatter branching structure with fewer longer term feature branches.

With a separate group you could support a more complex branch structure transparently to the developers. Which is both good and bad.

In all cases you'll need good tests to verify functionality.