It turns out the following command works well:

nv6000_smit stopall forceall

In fact the ovwexit command executed on a Netview client host from as an
rexec would not stop user GUIs.   Moreover, it hung up both the Netview
server and the Netview client hosts.  It turns out that the only way to
clear this up short of rebooting both server and client hosts was to issue
the command stopsrc -g nfs on the server host.