It's not actually the DC universe you want to avoid, here, it's the DC universe pretending to be the Marvel universe. :) Well, okay, quite possibly Lovecraftian Old Ones do regularly invade the DCU, but in this case I'm pretty sure that was Dr. Fate doing a real good imitation of Dr. Strange, who does tend to fight tentacled beings from dark dimensions. Barring a truly astonishing coincidence, the episode was a homage to a Marvel superteam called the Defenders, originally starring Dr. Strange, the Hulk, and the Sub-Mariner--you can see the correspondences, I'm sure. :) The smashing-of-things-and-refusing-to-talk felt very Marvel as well, although of course it's endemic to all superhero comics everywhere. :)

It worked very well as a Justice League episode, though, particularly Hawkgirl and Grundy, as you say.