Is this the first horror-comedy?

No, it isn't. The two genres had been mixing on celluloid for quite a few years before this film was made. It wasn't even the first old dark house film to heavily feature comedy - there had been quite a few from the subgenre to do so in the 1920s, including The Cat and the Canary (1927), The Monster (1925), and The Gorilla (1927).