Not sure exactly what you mean.  All the core ones would live in org.hibernate.internal.  We do need to be careful with OSGi however in that not ever module could define classes in that package :(

I do plan on documenting the logging *categories* (aka, "org.hibernate.orm.deprecation", "org.hibernate.orm.url", etc) in the logging topical guide.  

You mean a dev-centric document/guide on the different MessageLogger contracts?