Omen is Dilution's threat management tool of choice. It handles multiple targets and allows you to use different modes for tracking your threat. It will also sync data between other omen users, which is very nice for tracking the threat of those you cannot see, as well as seeing threat from actions that don't report into the combat log (sunder armor after stacked fully). Using other threat management tools is unacceptable as your threat will be incorrect for most targets.
Both of these addons do the same task, and for the most part are interchangeable. They are designed to notify you of events in bossfights, thus helping you to react quicker. They provide many avenues for notifications, and many times provide timers indicating when certain event will, or could, happen. As long as you are running one of these, you will be able to react much quicker and avid potential issues much earlier.
EP/GP is our current loot system. This mod will allow you to see real-time how you stand in priority for loot as decay/EP awards happen or people are credited loot with GP. It is not necessary to have this mod installed, all EP/GP values are stored and credited through officer notes, but it can become tedious to try to calculate priority on the fly.
Recount is a character performance tool, similar to DamageMeters, et al. It track damage/healing/cures/etc and allow you to review your performance against the performance of others. We do not believe that meters are the end-all for performance analysis. The fights that we face are trickier and trickier, so the person who heals the most isn't always the "top healer". Many fights require flexibility, and we realize that. That said, a tool like this is useful for comparing yourself when applicable, or certainly understanding what you might do to improve your numbers if they aren't what you expect.
We do encourage everyone to play at their maximum potential, and without SOME way to trend your performance, it gets tough to know exactly how you are playing.
There are many other mods we suggest using depending on your class and raid role, but these are the mods we that every raider with dilution should have.