Yes it is UDP based. The following is snipped from their page.
Any packet filter can pass realaudio streams.
If your firewall is based on that technology, it is a relatively simple thing to do. However, many sites prefer that random opening of UDP ports under the control of off-site machines not occur. And the base level design of realaudio requires that you open up a range, rather than a point-source port to receive the stream, since you can not predict the incoming side. And if you can't predict, based on standards, what incoming socket you need opened, then, I think, you have the potential for problems. Of course, with that development attitude, you have to wonder how well the rest of the product was engineered.