The Flesh Eaters FAQ says otherwise, specifically:
Q: If I have 3 Abhorrant Ghoul Kings on the battlefield, can I spend 3 command points to use the ‘Summon Menat-arms’ command ability 3 times at the end of the same movement phase?
Q: When I use a Muster ability for a Courtier, do I roll separately for each Courtier? And do I only roll 6 dice for each Courtier, no matter how many Courtiers are on the battlefield?
A: Yes to both questions. For example, if you had three Courtiers, you would pick one Courtier, then roll 6 dice and resolve the results for that Courtier, then move onto the next Courtier and roll 6 dice, and so on.
Q: Can any number of Abhorrant Archregents and Abhorrant Ghoul Kings use the Ruler of All He Surveys scenery rule for a single Charnel Throne on the same turn?
Pretty clear cut there I'd say, feel free to check for yourself though.