They do have some very similar characters to one another. Darkseid being similar to Thanos, bot large intergalactic gods bent on destroying universes, Deathstroke/Slade and Deadpool, both have similar masks, guns, and katanas, but Deathstroke is a supervillain and like Harley Quinn, Deadpool is an antihero. But I think Teen Titans Go!, The LEGO Movie 2, and The LEGO Batman Movie had some very interesting references between DC and Marvel, despite that these movies and TV shows are DC material. Batman in the LEGO universe has a password to his Batcave that says “Iron Man Sucks”. The LEGO Movie 2 reference that the Marvel figurines were busy, when the gang were captured by the DUPLO aliens. Teen Titans Go! does have some very clever Marvel references, they said an example that Spider-Man would never fight Darkseid, when the Justice League were captured. They did also have a bundle of Marvel references throughout Teen Titans Go! To the Movies, the Titans were mistaken for the Guardians of the Galaxy by Balloon Man, but with Raven correcting that was a different superhero universe, because they’re in the DC universe, they called Slade Deadpool, but Slade saying that his debut came out before Deadpool even existed, even Cyborg made a reference on the Deadpool movies, and even during a fight, Beast Boy called him Deadpool once again. Also Stan Lee made two cameos in this movie, in his first debut in a DC movie (where the Titans explore Hollywood aka Warner Bros and Stan Lee was doing hero poses, but was stated that he’s in a DC movie, not a Marvel movie, and he also appeared again, when the Titans were on a golf cart escaping the hypnotized DC superheroes from destroying them and also exclaiming “excelsior”, right until they had a plan to save the world from Slade’s control). So they definitely do have some similarities and differences, plus a Spider-Man crossover with Batman and Teen Titans Go! vs Teen Titans was an interesting reference to Spider-Man: Into the Spider-verse (which came out in the exact same year as Teen Titans Go! To the Movies) with a Multiverse full of different teams of Titans, especially their alter-egos throughout Teen Titans Go!, other than Teen Titans and Teen Titans Go!.
Here is a time where Iron Man is referenced in DC:
Two tangentially connected thoughts:
Watchmen existed in the DC universe before it was a part of the DC universe. Notably the Question reads it and tries out Rorschach’s style before concluding that “Rorschach sucks.”
Vertigo also existed as comics could be seen in stands from time to time.
There are references to Marvel but they tend to imply Marvel is a part of the universe rather than a fictional company. My personal take is that, back in the day, Marvel was struggling and DC was doing really well. DC was buying up comic companies at the time and I think they had an eye on Marvel in the long run. They implied it was part of the universe to leave it open ended. Nothing to back that up but it explains some. More recently, Marvel is not struggling so this is no longer the case unless DC is optimistic to a fault.
Some fun nods over the years though. A favorite of mine that hasn’t been mentioned above is a inter dimensional assassin who attacks Clark and Bruce on a boat (Ultraman and Owlman also show up). The assassin looks a lot like Deathstroke but is much more chatty and gets interrupted everytime he tries to say his name. He keeps trying to say “Deadp—”.
There are a few dc/marvel crossovers including Superman vs Spider-man, DC versus Marvel Comics, and JLA/Avengers. For the full list look up dc and marvel crossovers and a link for a dc fandom page should show up.
To answer your specific question, yes marvel has been referenced here and there.
Robin mentioning Peter Parker aka Spider-man.
When he says “guy in armor” he means Tony Stark aka Iron Man.
An Interesting cover…
The second one clearly means Marvel exists as a comic, and that matches tge other 2.
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