I tinkered some more and got it to work by removing "value" elements that enclosed the util:list elements. In other words, like this:
<bean .... >
...
<property name="monitoredObjects">
<util:map map-class="java.util.HashMap">
<entry key="java.lang:type=GarbageCollector,name=ConcurrentMarkSweep">
<util:list>
<value>HeapMemoryUsage</value>
<value>NonHeapMemoryUsage</value>
</util:list>
</entry>
<entry key="java.lang:type=FOO,name=BAR">
<util:list>
<value>YADA-YADA</value>
<value>BLAH-BLAH</value>
</util:list>
</entry>
</util:map>
</property>
...
</bean>
Thanks as always for looking!