I just booked a meal for a party of 11, and I did it through the regular dining phone line. This was only one meal though, the rest of our ADRs are for 3-6 people. If I were you, I'd try calling the regular line and see what they say.
for our party of 8 on the regular dining reservation line. There was only restaurant where they told us we would have to have 2 tables -- and when we got there, they put us at the same one anyway. We didn't have any problems for that size group.
I've been booking between 10 and 15 people for our upcoming trip and just called the regular number. If they think you need group dining they transfer you over.