Yeah, that was sarcasm. The season 6 episode "Who Mourns For Morn?"
is all about him. The big joke in that episode is that Quark says Morn never stops talking, but we the audience never see him say anything.
He is just a funny background character. There was a famous show in America called "Cheers"
about people in a bar who are friends. One of the most popular friends was named "Norm". Morn is a joke reference ("Norm" backwards). A lot of people like Morn (including me) even though he doesn't talk because his make-up is cute and it's nice to see him always sitting at the bar.