Jetty can be monitored via JMX which SAM supports natively. I would recommend following the steps outlined here and then using the "Find Processes, Services, and Performance Counters" wizard under SAM settings to browse the JMX components available through your Jetty server and build a custom Jetty application template.
The JMX monitor comes with APM 4.2 and above, which = SAM 5.0 and above. You can find it in the web console under Settings > SAM Settings > Component Monitor Library > JMX Monitor
