Yes. We sent them the measurements, weight & a tracing of the "footprint" of the castle. They said it will be no problem, though it sounds as if they will build support into the cake to hold the weight of it. We also had Meri include on the BEO the measurements and weight. Oh, and we are doing a 2 tier cake and the top layer will be made large enough for the castle, even if it is bigger than the size we'd normally have for the top tier. Since we are serving one piece of each layer to every guest, it worked out fine that way. I hope that helps!
BTW, I hope you can find the castle. Disney merchandising told me I had one of the last 2 available at the warehouse and then my friend and I saw one more at the outlet and they said it was the last one and she was lucky to get it. So, if you can't find it elsewhere, check Disney merchandising and lenox. Good luck!