It may be a very good ideea to use Nullable or Null prefix for the aliases of the generic types. Some people (or at least me) move all namespaces to the using section and this would definely lead to compiling error because of ambiguity.

Currently there is MyNHibernateContrib.Nullables.Int32 for example, I really think it would be better like MyNHibernateContrib.Nullables.NullableInt32 or MyNHibernateContrib.Nullables.NullInt32 or any other combination.

You may create a JIRA issue about this... (and vote it)

But I am not sure it will ever get done as it would be a breaking change and it doesn't look like many people will benefit from this change.