Whilst we are talking about validations, I should mention that ValidateThis, my validation framework for ColdFusion objects, works perfectly with CF9 ORM-based objects. I've not read all of the docs for the Hibernate validator, but from what I have read, ValidateThis provides most of its functionality, and even some extra stuff that is specific to developing HTML-based CF aplications.
One of the things that VT does not currently provide is for defining validation rules via annotations. Currently you must either provide them in an XML file, or programmatically via CFML. I do plan to add the ability to define validations using annotations in the very near future, as well as some other features of Hibernate validator, such as cascading validation.
Regarding using the Hibernate validator with CF ORM, again, this is just based on a cursory look at the docs, but it looks like the validation rules are baked into the java class itself, so that might be one technical hurdle. Also, the results returned when validating are all java objects, so I imagine, if it is possible, that it would involve writing a bunch of Java code. One would have to wonder, if that is the case, whether there would be any point in trying to use it with CF ORM, or whether it would make more sense to simply write your whole domain model in Java or Groovy with Hibernate.
Cheers,
Bob