Maybe not for your visit, because the last time I had one and saw one it was at the Blue Ribbon Bakery which may open mid June. There is also a cupcake store opening in DTD, it may be open by now.
They do indeed have red velvet cupcakes at the Cupcake Kiosk by the DTD AMC theater.
While they have red velvet cupcakes occasionally at Marceline's, I tend not to like Disney cupcakes very much - highly disappointed with the ones for Mardi Gras. I do like the ones from this kiosk and we rave about them on the show.