Конечно. NHibernate может загружать hbms практически из любого места:
public class Configuration
{
public Configuration AddAssembly(Assembly assembly);
public Configuration AddAssembly(string assemblyName);
public Configuration AddClass(Type persistentClass);
public void AddDeserializedMapping(HbmMapping mappingDocument,
string documentFileName);
public Configuration AddDirectory(DirectoryInfo dir);
public Configuration AddDocument(XmlDocument doc);
public Configuration AddDocument(XmlDocument doc, string name);
public Configuration AddFile(FileInfo xmlFile);
public Configuration AddFile(string xmlFile);
public Configuration AddInputStream(Stream xmlInputStream);
public Configuration AddInputStream(Stream xmlInputStream, string name);
public Configuration AddResource(string path, Assembly assembly);
public Configuration AddResources(IEnumerable<string> paths,
Assembly assembly);
public Configuration AddUrl(string url);
public Configuration AddUrl(Uri url);
public Configuration AddXml(string xml);
public Configuration AddXml(string xml, string name);
public Configuration AddXmlFile(string xmlFile);
public Configuration AddXmlReader(XmlReader hbmReader);
public Configuration AddXmlReader(XmlReader hbmReader, string name);
public Configuration AddXmlString(string xml);
}