Gert,
While this may work with Snap Creator, it is not supported by IBM.
http://www-01.ibm.com/support/docview.wss?uid=swg21472690
Unless otherwise noted by a specific Notes or Domino subsystem, UNC pathnames are not supported for use with Notes and Domino. Support of UNC pathnames is being tracked under SPR GFLY6X9RME. This SPR tracks existing known areas of incompatibilites with UNC pathnames and calls for support of UNC pathnames. There may be certain subsystems within Notes and Domino which are able to handle UNC pathnames and therefore will support them - such systems will have their own technotes indicating such support.
Definitely not recommended.
Thanks,
John