So, is this some sort of mating thing? The shubunkin doesn't bite or
pick at them, just loves to push them around. I find the other goldfish
hiding (and panting heavily) in the veggie filter. If the shubunkin
finds them he will root them out, or sometimes just wiggle in beside
them. That's what made me think it was a mating thing.

Yup - you got it - the Shubunkin is a male and those that he is nudging and
pushing around are females, trying to help them release their eggs so he can
fertilize them
Gale :~)