In the United States, I'm betting, they're overwhelmingly white males, with a majority conservative in politics. And now you know another scheme to corral the general public towards a Trump win. Why are they doing this? I could tell you, but it would take a while and you need to be somewhat awake.
Maybe it's just my market, but whenever I see an Uber placard it's typically a white male. I suppose I can't generalize that to the nation, not sure what you all are seeing, but I bet a poll here would get us a rough guesstimate.