Short and simple?
After you kill the last boss of the tier should there be scrolling credits (that you can skip ofc) transparent ofc.. so you can see who was a part of that raid. at current we have no clue who did what or how many people it took to bring a raid together.
People who work for blizzard can't really say to their next employee they worked for blizzard as their is no in game proof.
What is your view? end of the expansion after you kill the last boss or for every raid at the end of the raid?
http://wowpedia.org/Credits_of_World_of_Warcraft this lists everyone working for Blizzard but it does not for example, who voiced thunder bluff npc #23 or w/e