More information, if I turn -Dlog=debug I can see the process hanging as follows:
INFO [main] [SQLQueryMeasurementPlugin] Registered proxy for domain: sql
DEBUG [main] [ControlPluginManager] PluginNotFound creating plugin for service 'scott_service' from server 'NetworkServer'
DEBUG [main] [Collector] Adding exec collector: [/h/COTS/HYPERIC/agent-4.6.5.1-EE/bundles/agent-4.6.5.1/pdk/scripts/scott.pl]
Never returns.