I'm not sure on the union front, I've certainly known several who are UCU members. I'm not aware of any who are Unison members but it's not widely discussed. I only knew of the UCU ones when they went on strike! My understanding is that UCU are supposed to represent all staff above a certain grade whether academic or PS, member or not (but in reality they aren't interested in anyone who isn't paying subs, IME).
I think there seems to be a significant number in either group who are GI but then we probably notice them because they're the ones with the pronouns in signatures, proclamations that they're an "Ally" etc but I suspect there's a lot more who either don't really care or who are quietly GC but don't want to put their head above the parapet. I'm definitely the latter group, I don't want people turning on me!