Turns out that won't be a problem. I got a call from the event manager and the final word is that my best bet, even though I'm booking 10 rooms, is to book them in groups of 3 online, as the standard offered-to-everyone rate the best they can do.

I understand that 10 rooms isn't a big chunk, but at the same time, I don't know why I can't use the event folks to reserve the rooms. They can give me the internet rate w/ no discount, that's OK I guess, but why make me go to the hassle of having to go through four sets of reservations (3, 3, 3, 1) to get the rooms? Either open up the website to let me book 10 rooms at once or allow me to get the same rates when working with the group rates people...