OpenAccess is not based on NHibernate at all. It is an independent ORM, so basically an alternative to NHibernate.
Please have look to our key features to learn more about the major advantages you would get with OpenAccess. We recommend to test it (registration/login required) with your use cases and in your environment.
Additionally you can expect first class support from Telerik.
Please do not hesitate to contact us again for any further question.