Hi Jean,
Sorry for the late answer but you might want to look at the option "ndmpd.preferred_interface".
This will work for Snapvault.
For Snapmirror, you will have to do that from the configuraiton files /etc/hosts and /etc/snapmirror.conf.
You will insure to have proper resolution of the hostname with the desired IP and then specifify in snapmirror.conf the newly created hostnames for the source and destination.
If you have multiple free network interfaces, you can use them too, but I would advise you to go through the documention or TR in research for the configuration term "multi".
Hope this will help
Rom;)