1) "i have the lest jboss tools and eclipse 3.5.1, i suddenly noticed that if my hbm is not valid by the dtd i don't get a report in the xml editor, only in the tree editor. "
this could be a bug - please create new issue here: https://jira.jboss.org/jira/browse/JBIDE
try to make it more descriptive - for example your hbm.xml example file is necessary.
2) "another problem i've stubmled upon is the use of entity reference causes problems with tree editor which does not recognizes it." - also look like jira issue
3) "attempting to generate a graphical schema fails with classNotFound of one of my enums (a real enum) even though it's in the classpath" - don't understand exactly, if you mean Hibernate Diagram Viewer - could also be a bug - create jira issue.
4) "and is schemaexport function working correctly?" - what is your expectations here? generally it works correctly, with our intention.
in general all Hibernate Tools (part of JBoss Tools related to Hibernate) questions you could ask/discuss here: