Yes, you can do the extension filtering that is described in the Programming Guide, using a custom property like myVmProperty below whose value will be returned by your own PropertyProviderAdapter.
<metadata>
<objectType>VirtualMachine</objectType>
<propertyConditions>
<com.vmware.data.query.CompositeConstraint>
<nestedConstraints>
<com.vmware.data.query.PropertyConstraint>
<propertyName>myVmProperty</propertyName>
<comparator>EQUALS</comparator>
<comparableValue>
<Boolean>true</Boolean>
</comparableValue>
</com.vmware.data.query.PropertyConstraint>
</nestedConstraints>
</com.vmware.data.query.CompositeConstraint>
</propertyConditions>
</metadata>