Yes, that was during the episode future-drama (which actually was a non-canonical episode anyway i think) where in the future, bart and homer drive through a "quantum tunnel" which is where they meet bender. So really, a crossover COULD happen if the creators decide to muck about with reality (which is i believe what occurred in the comic crossover)
also:
to answer rick jones
The "hallucination" happened during a seperate episode, in which bart loses his mind from watching too much tv. Various tv characters (which include bender and a knock-off of pikachu) appear in his classroom replacing some of the students. Then a clown appears and says "its finally happened bart. you've lost your mind!"
What you thought was a hallucination actually happened as i mentioned above.
and finally, for visky
yes that also happened.