regarding your own comments: don't mix form configs & doclib configs!
org.alfresco.web.config.forms.AspectEvaluator is the Evaluator for form configs like
<config evaluator="aspect" condition="my:parentAspect">...</config>
org.alfresco.web.evaluator.HasAspectEvaluator.java is used for aspect-related evaluator within
<config evaluator="string-compare" condition="DocumentLibrary">
e.g. for indicators, metadata-templates etc. So, org.alfresco.web.config.forms.AspectEvaluator is the one here. It's a subclass of org.alfresco.web.config.forms.NodeMetadataBasedEvaluator that uses the api/metadata Webscript to get the Metadata of the given node:
/api/metadata?nodeRef=" + nodeString + "&shortQNames=true"
This webscript uses org.alfresco.repo.jscript.ScriptNode.toJson() which only includes directly attached aspects.That could be your starting point for a custom Evalutor.