Under OS X, if you log into a server for your home directory, then you cross over into the network via /private/server_name/users_folder ...
so you could enumerate the path to the Home Directory and test to see if /private is one of those paths, if it is, then you know that the user's home directory is on a network volume. Also your other connected volumjes digg deep into private. You'll have to view it yourself and figure it out.