GREENWICH - A group of Greenwich campers spent their summer sharing the stage with special needs youths. The Off-Beat Players, an arts camp that includes young adults with and without disabilities, was founded five years ago by Executive Director Kim Malara. She is a special education teacher by trade. As its annual musical, the cast of 35 put on "Urinetown," a comical tale about a community that bans all private toilets and requires residents to pay for public facilities. The playwright learned of the program and invited the cast to perform on the off-Broadway stage where the musical debuted in 2001.