This isn't quite as simple as swapping out the Tomcat bundles for the Jetty ones. There's no standard API for bootstrapping a servlet container so both Tomcat and Jetty have their own. dm Server includes some code that bootstraps Tomcat and provides some custom configuration to ensure that Tomcat works nicely with OSGi classloading, etc.
My advice would be to wait a little while for project Virgo to getting going at Eclipse.org. Given that Jetty is an Eclipse project now, I think it's likely that the Eclipse community will be interested in getting this to work.