Bongino has shares in Rumble, an upstart video platform. He doesn't own anything in Parler.
Nothing wrong with using your opponent's platform to grab business for yourself.
Actually, there is something wrong with it. It means your own platform sucks so you still have to suck off the teat of the guys you want to knock off. Look, I hate Jack Dorsey, the guy's a total douchebag, but Twitter revolutionized online communication and is one of the greatest communication inventions since the printing press. Don't hate the player, hate the game.
TV networks do that all the time.
Where? No TV networks do cross-advertising unless it's for playoff sports. They might cite other networks for a story, but they don't do what you are citing.