It's possible just other usages of "im Urlaub" elevated, like "im Urlaub erlebten wir das und das", "im Urlaub hatten wir schönes Wetter" and so on. "In Urlaub" as in currently becoming there, seems totally Mistaken in Upper-Austrian, but I don't know about the Germans. I've also heard of "auf https://bihlmayermedia-bilder.com/urlaub/wir-sind-im-urlaub/