Even if they don't split the plates themselves, if someone orders an entree and someone else orders just an appetizer and you ask for it all to be brought out together, you can probably do it yourselves.
Yes, they will absolutely bring an extra plate. DH and I had no trouble at all splitting a meal there or any other restaurant at WDW in June. We didn't do any buffets or family-style meals (obviously this wouldn't work at those places), but everywhere we did go, we had no problems. The portions there were huge!