Your .NET application can include C++ portions, so you can also use ObjectARX APIs that do not have managed wrappers. The ObjectARX managed wrapper classes have a consistent property and method that enable you to go back and forth between the managed and unmanaged object.
A pointer to the underlying unmanaged object from a managed object can be obtained using the UnmanagedObject property. You can create a managed object from an unmanaged object with the DisposableWrapper.Create() method.