Yeah, 9/11 happens in both Marvel and DC continuity

It's pretty great because in the Marvel 9/11 special, even the supervillains cry about it

Supervillains who all, at one point or another, have blown up the WTC themselves or had plans to

Hell, I still have my copy of X-Force where Juggernaut and Black Tom Cassidy blow up tower 1 and laugh about it

Also one of the earliest appearances of Deadpool, from before Fabian Niceiza actually made him a character