Does he have a hype man or is SNL starting some sort of stupid “somebody’s gotta dance with the musical guest star” schtick?
He is a part of Beck’s band. And apparently, dancing and banging on that garbage can are all he does.
I wasn’t sure. Because if anybody would have a hype man, it would be Beck.
I only caught “Summer Girl” but I thought I saw some keyboards over to his right. Maybe on other songs using keyboards, he plays those?
Heh. I only watched SNL through most of the first Beck song, but I found myself wondering (out loud, even), “What’s with the guy in the jumpsuit?” 
Back when Ska was almost getting popular, there were several bands with a Dancing Dude. Beck’s musical genre sometimes comes across as a mixture of Alt Rock, Ska, Faux Punk, etc… (he’s hard to pin down). Maybe he picked up on the use of Hype Men in Rap and Dancing Dudes in Ska and just felt like adding a similar thing to his brand of music.
Good theory, no?