Childish Gambino, The Rock, Will Smith don't come to mind, breh?
First off, acting ain't shyt. Literally the easiest job on Earth.
While I'm not completely familiar with Donald Glover's career (I only know him from Community

), I can tell you The Rock and Fresh Prince were a wrestler and rapper, respectively, who then transitioned into acting once they built a name for themselves. Will Smith landed the Fresh Prince of Bel Air without ever acting in anything. And isn't wrestling acting anyway?
In all honesty, entertainment is entertainment. If you can get in front of a crowd and entertain them in any way, you can easily add acting. Athletes, musicians, politicians... we've seen every type of celebrity also act. You think of Ludacris as an actor? He said it himself, they give him a boat load of money so now, yeah, he's an actor he guesses.
What you're describing, I wouldn't call classical "multiple hustles." That's just a classic case of the rich getting richer. If you have money, it's easy to make more money. But The Rock's craft was wrestling. He mastered that then parlayed it into an acting career. Smart, since you can't wrestle forever. Prince was a rapper. That was his craft. Quincy Jones saw his charisma and decided to put him on TV. But if he never mastered his craft, we might have saw Kid and/or Play on that show instead.