This is similar to what DC pulled in Trinity, when they referenced events from JLA/Avengers.
During a flashback scene in Trinity #7, Krona(as he appeared in the crossover) used the exact same dialogue he used in the crossover...
Krona: "NO! NO! No, you can't -- My power! Not while I still haven't--":
http://i.imgur.com/yfOfyGZ.jpg
Here's the exact same scene/dialogue from JLA/Avengers #4:
http://i.imgur.com/RKhuO1F.jpg
http://i.imgur.com/oMirgO3.jpg
Furthermore, the scene from Trinity also makes an indirect-yet-direct reference to the Avengers being present:
"He was so close--and then torn from the universe again, ripped apart--The League was there, The League AND OTHERS--":
http://i.imgur.com/yoJjZ1T.jpg
See? Even DC has mentioned the events of a crossover between the companies, without directly infringing on any copyright laws.
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Here's another example from Superman v2 #50...
Mxy: "Here I am, having fun with my Fantastic new friends...":
http://i.imgur.com/XkUtE9m.jpg
Mxy: "Okay... Now that that's done... Back to my Four new friends."
Then, just before assuming a form very similar to Impossible Man, Mxy states: "Oops! Almost forgot... Sometimes it's just Impossible to remember what I look like from world to world!":
http://i.imgur.com/8SCZLoR.jpg
So yeah, Mxy was shown clearly impersonating Impossible Man, and clearly heckling a version of the F4. But again, DC only made a few indirect-yet-direct references to Marvel, as to not infringe on any copyright laws.
There are other examples, but you get the point. Were any characters/names from other companies specifically mentioned? No, that would have ended up with litigation. However, we as readers don't need explicit character references to still know what is going on.