Yep, I've seen that also, however I am not sure how accurate that information is. First of all, the VP4001 has a round top where the controls are and the DT-500 and XV-Z3000 has a rectangle top. Also, if it is just a rebadge, then it would mean the optics in the XV-Z3000 is also a Marantz Custom optics which I am not certain about since the xv3K has some CA. Also, according to Marantz literature, the technology inside the VP4001 was based on technology originally developed for Marantz's VP11S1 projector. If it was a straight re-badge, then that would mean also that the XV-Z3000 had this development benefit. Right now, if it is just a re-badge, I am just glad about the 3-year Marantz warranty that comes with this PJ.
It appears the casing is probably very well engineered especially with the heat sink and lot of other manufacturers are using the design, like EIKI and one other I am forgetting about.