Collegiality is a sticky issue, because if two people don't see eye-to-eye, which of them is being uncollegial? A lot of us have intense, difficult personalities, might not be naturally easy people to get along with. When conflicts arise, it is hard to know who is to blame (for example, between two people who are both somewhat difficult.) There might also be legitimate differences in opinion / ideology that make things more difficult, or difficult work conditions. If the administration puts the squeeze on a department, some might react by siding with the administration, while others might legitimately resent them for that. I have friends in various departments who don't like other friends of mine, even when all parties concerned are dedicated professionals. I also don't know if I would be as good friends with certain people if I shared a working space with them.
The problem with using collegiality as a criterion for promotion is that the largest burden should fall on the senior colleagues. In other words, if a junior colleague is perceived as uncollegial, often that is in reaction against treatment by the senior colleagues. They shouldn't be able to mistreat the person and then turn around in call the same person uncollegial for fighting back. I remember that feeling that the senior colleagues are not on your side, and since I got tenure I've tried very hard not to be that guy. I am still in the position of judging the untenured people, and every one knows it, but usually if a senior colleague positive then junior people will not go out of their way to make enemies.
In short: the senior colleagues should set the tone. Some conflict should be expected; not everyone is going to like everyone else. You shouldn't take sides in other departments unless you have an extremely good sense of what's actually going on.