An offhand mention in a recent episode discusses the Jedi fighting against the Mandalorians and the outcome of that war, which was a major point behind the setting of KOTOR (since Revan and Malak were heroes of that exact war) and hints that there may be some canonicity to those events after all. It’s the sort of teasing at canon that Rebels has engaged in before now, with the Hammerhead corvette from both the show and Rogue One serving as a direct nod to the Hammerhead cruiser from KOTOR, but this is a more explicit reference. It’s fun to speculate about for lore nerds, at least.
Star Wars: The Old Republic is not canon. It was one of the many things caught in the Star Wars Expanded Universe purge, which helpfully took every Star Wars novel, comic, radio play, video game, and limited-edition narrative candy wrapper and made all of them non-canon. All that’s canon is the stuff that appears in the films and the television shows, and everything else is wholly speculative, which means that canon loses an enormous amount of terrible fiction and a small amount of really good fiction. Except that now the Star Wars: Rebels series is teasing that Star Wars: Knights of the Old Republic may, in fact, be canon after all.