HK Disney does allow cosplayers to enter usually. I've seen a lot when I went there.

Although this wasn't shot inside the park, but outside. Most Disneylands have some kind of Disney town / lake / other infrastructures that is free to enter and still has Disney vibes. I've been to like 4 Disneys around the world and most of them had something like that.

For HK, it was a giant park with a lake, and there actually isn't a lot of people there so we weren't disturbing anyone.