Certainly possible, if it would have been unnecessarily difficult to make it all in a single mold...
The back piece seems to be separate, to allow for access to the lighting, I assume. Looking closely, there appears to be a small gap between the black interior body and the silvery external shell, which makes me think the heroes are maybe cast in multiple pieces (back, front shell, front black parts)? Additionally, they seem to have something like clear beads in them, visible through the 'windows,' and maybe 'glass' in the windows to keep the beads in place, if they are loose, and not cast in clear resin as solid inserts.
The background Hydra 'bandoliers' are vac-formed, but the heroes appear to be multiple parts, maybe even all illuminated.
I found a guy online who worked on some of the big Hydra ray guns. I reached out to him on FB; I'll see if he has anything to say re: the battery.
-MJ