Currently, our Web Services support does not permit the saviing or Persistence of Business Objects. This is scheduled for a future release. If you use the Persistence Manager directly, and you were using IIS, you would either be using Remoting or WCF.
I believe that you should be able to ise WCF to perform RPC.
There is nothing that I know of concerning Notification Services that limits them to dealing with database changes. Notification services for databases should not be restricted to SQL Server. However, I don't know of, for example, any offereings yet from Oracle,