Yes, things that Beyonce does with other artists will help their career. Getting any press with Beyonce is bound to help an artist's career. It does not make sense to believe that it will not help someone's career to be snuck up on by Beyonce whether for a good or bad reason.
Beyonce's mere presence does that to people. She gave everyone in that room so much life that they laid in awe after she performed. unable to grasp the perfection they just witnessed.Beyonce is literally the only person in the universe who doesn't get absolutely eviscerated in the comment section of a Buzzfeed article about them. And I'm not mad about it.
Anything Beyonce touches turns to gold, so anyone she associates with is likely to get a boost from a show of her supports. Chance has skills anyway, but isn't widely enough distributed yet. That is going to change when record executives and fans see Beyonce is also a fan of Chance's work.
Beyonce is very popular. Chance the Rapper is less so. That Beyonce thinks that Chance is important enough to sneak up on at the VMAs will only help his notoriety. Even if Beyonce weren't the icon that she is, the fact that Chance got any attention in that kind of forum will help his career.