Just recently finished V4 and I’ll share my take. The ventriloquist dummy is not “Roger”. From context it seems “Rodger“ is another powerful being similar to the collector or the Dark tree god. He has no form so he can not live on his own and needs a conduit, hence his many human vessels that carry him around. The dummy is most likely what he prefers to ride around in to avoid suspicion. This can also be seen at the end of V4 when Spencer pulls the doll off Rosa’s hand and destroys it. Because he touched it he became the new host to the formless being. He then removes his sock and uses it as a puppet for Rodger to speak through. So basically the puppet does not imply another person in the story is hiding his identity using dummy, rather the being known as Rodger has no true form and uses dolls, dummy’s, and other items as conduits attached to humans. side note, we’ve already see other gods demonstrating the importance of human conduits aka Rosa. The dark tree god used Rosa the same way Rodger used all those other people that carried him.