Whatever else happens in Zack Snyder's career, it seems a foregone conclusion that he will forever be remembered for Justice League, both the theatrical version he started and his own version that was recently released on HBO Max. Snyder has been a big part of Warner Bros.' attempt to create it's own cinematic universe to rival Marvel, but just because he's so closely associated with DC characters doesn't mean he has no love for Marvel. He's a fan of the House of Ideas as well, and he's a big fan of two Avengers.
Zack Snyder recently took part in a video for Wired where he answered questions asked by looking at how Google queries would autocomplete. This resulted in a number of interesting questions, about who Snyder's favorite director is (John Boorman) and if he is a Green Bay Packers fan (yes). But it also asked whether Zack Snyder even likes Marvel. Since Marvel and DC are supposed to have a rivalry, it's possible that Snyder is very much on Team DC, but he admits that he's a fan both of Marvel Comics and the Marvel Cinematic Universe, and he mentions two characters that he has a particular affinity for. According to Snyder...
I do like Marvel. I love Marvel movies and I like Marvel comics. The Hulk has always been one of my favorites forever. And Iron Man.
Iron Man and Hulk are two solid picks for favorite Marvel characters. I'm not sure anybody who has followed Marvel hasn't been a big Hulk fan at one time or another, and certainly after what Robert Downey Jr. did for Iron Man it's difficult to not be a fan of his.
While there is certainly a rivalry between Marvel and DC, it's largely a friendly one at this point. While there are many who might need to choose between buying a Marvel or DC comic or seeing a Marvel or DC movie, there are just as many who enjoy both equally. Zack Snyder probably likes DC more than he does Marvel, that much seems clear, but that doesn't mean he has to dislike the other side.
And we're starting to see people work for both sides of comic book divide as well. Zachery Levi played a character in Thor: The Dark World before going on to play Shazam!. And James Gunn directed two Guardians of the Galaxy movies but has also now directed The Suicide Squad which comes out later this year.
Could we see Zack Snyder work for Marvel? It's probably a long shot, but it's certainly not impossible. And if he's a huge Hulk fan, maybe Snyder could direct a new Hulk movie. We absolutely need one of those, and somebody needs to helm it, and a director who is also a fan would be a great choice.