Yes, in America we say "on a team" quite often. E.g., "John plays on our high school's basketball team."

I think "on" and "in" have slightly different meanings here. You would could say "I am on the soccer team" but not "I am in the soccer team". You could say "you have to work in a team", but usually not "you have to work on a team." I think generally you work "in" a team, and you play "on" a team.

on here means "belong to a group or organization"