I do vibrato slightly differently on bent notes compared to non-bent ones. How I bend effects the vibrato action, too, because it's kinda the same motion, just smaller and faster.

To bend, I pivot my hand on the first knuckle of my first finger (the one right at the palm). I twist my wrist, too, like I'm turning on a tap. You really don't wanna bend just by pushing your fingers up.

When I'm vibratoing a non-bent note it's much the same action, but my fingers do a tiny bit of the work as well.