I guess we won't know for sure until someone gets their hands on one. It seems logical that the bass he demos, with the pickup that matches the one pictured in the blog, would be the same. What doesn't seem logical, is that Gretsch would expect to sell many basses with such a non modern sounding pickup. Maybe Scott can clear up the confusion?
*edit: I realize the pic of the four string wasn't from the original blog. All the same, it still seems like the rumbletron will be a mudbucker based on it's description and the available images.