This film has been a seminal influence in my work - along with Laurel & Hardy's "Bohemian Girl". As a kid, watching it for the first time on Elwy Yost's "Passport To Adventure" (which had a similar format but predated his "Magic Lantern" series) the Bogey Men scared the living shit out of me.
I have since been a huge fan of Henry Brandon, who played "Silas Barnaby", the Crooked Man. He was actually just a young guy when he played this part and had a history of performing in Yiddish theatre where he acquired the affected style of extreme theatrical melodrama that so suited the part of Barnaby.
As for the Mickey Mouse / Monkey. Yeah - that was disturbing for a kid. Definitely crossing the uncanny valley. Not a mouse - is a mouse - is a monkey - isn't a monkey - WTF? But yes - it was a Monkey in a Mouse Mask.
The interplay between the Mouse and the Cat was a direct steal from George Herriman's "Krazy Kat" - complete with bow on the Cat and the Mouse chucking bricks at it.
The Mouse was obviously styled after Mickey and I would be surprised if it was actually an unlicensed usage - especially since they also used the very popular Disney music for "Who's Afraid Of The Big Bad Wolf" for the Three Little Pigs sequence in the film. I'm pretty sure Hal Roach got the necessary permissions to use both a likeness of Mickey and the 3 Pigs song - because otherwise, Disney would have had Roach's ass mounted on the wall of his office.
It's worth noting that Disney did their own version of this much later - in 1961, with Annette Funicello, Tommy Sands, Ed Wynn and Ray Bolger. It really fucking sucked.
Both were based on the Victor Herbert operetta but the Hal Roach version with Laurel and Hardy was far superior - as was the truly fucking amazing Bohemian Girl. Both of these gems were big budget affairs for Roach and the sets were amazing, providing a black & white run for the money on anything Wizard Of Oz came up with later - and for a lot less cash, I am sure.
I was under the impression that this film was actually firmly in the public domain - as is Bohemian Girl - but perhaps (and it's understandable considering all the demented legal bullshit surrounding such things) I am wrong. Regardless, and without any contractual documentation to back me up, I think it's pretty plain that the use of Mickey Mouse (disguised as an uber-freaky nightmare inducing Monkey in a mask) and the Three Little Pigs song was properly licensed for use within this film production.