Ullman's first professional role was as Louis in the national touring company of The King and I along with Jesse McCartney. Other productions he worked on include Peter Pan at the Polka Dot Playhouse, The Music Man with the New England Repertory Company, and Just People at the Long Wharf Theatre. He received a 1998–1999 Best Actor nomination from the Connecticut Critics' Awards for his character Stanley in Stamford Theater Work's A Rosen by Any Other Name.
Ullman is best known for his starring role as Phil Diffy, a teen from the year 2121 on Disney Channel's Phil of the Future, a series that debuted June 2004. He also starred as Roscoe in Disney's made-for-television film Pixel Perfect and as Sam in ABC Family's television film Searching for David's Heart (2005). Ullman was an identified member of the Disney Channel Circle of Stars, and appeared with other members of the Circle in the music video for "A Dream is a Wish Your Heart Makes," where he sang as well as played the drums. Ullman also appeared in the Law & Order: SVU episode "Obscene," in which his character rapes a teen star (Maggie Grace). While Ullman previously went by the stage name Ricky, he started using his real name in 2006 when he guest-starred on an episode of House and continued to use Raviv on all projects since. In 2008, he appeared in an episode of the television series The Middleman.
He played the character Kip in the sitcom Rita Rocks on Lifetime. He is Rita's daughter's boyfriend and plays the drums in Rita's band. The show was canceled after two seasons. Ullman was later featured in a television commercial for State Farm Insurance alongside John C. McGinley and in a commercial for Cox Cable. From January 2012 to March 24, 2012, Ullman starred as the character Alex in the New Group's production of Russian Transport Off-Broadway in New York. On April 30, 2012, it was announced that Ullman joined the cast of Alena Smith's new Off-Broadway play The Bad Guys. It began performances on May 22 at the McGinn/Cazale Theater on the Upper West Side in New York City.
Ullman speaks fluent Hebrew and keeps kosher. He lived in Southern California with his friends, two of them being Lisa and Jess Origlasso from the pop band The Veronicas. He resides in New York City.