We book all our ADRs for 8-12 people and usually have no issues. I remember having to call once due to the large number - I’m pretty sure it was Rainforest Cafe. I usually book Rainforest Cafe directly with them and not through Disney dining anyway, though.
We’ve booked many restaurants including Akershus, BOG, Ohana, 1900 Park Fare, CRT, Hollywood & Vine, Crystal Palace and more for a large group online without having to call.
What restaurant were you looking for?