Hello CendresMetaux, I am not aware of any Isilon/PowerScale internal services that require generic DNS. Have you looked at the PowerScale OneFS Security Configuration Guide? Here is the link to the guide. [URL]
Could I define a dedicated groupnet solely used by the System AZ for cluster management tasks, where the SyncIQ target cluster SSIP is defined as DNS server for the SyncIQ source cluster and vice versa? No AD/LDAP/NIS/whatsoever integration intended, local users/auth only (mgmt purpose). After checking firewall logs, it seems that the Isilon/PowerScale clusters are not querying a lot of DNS and the queries they send seem to coincide a lot with our SyncIQ schedule. Do you know of any Isilon/PowerScale internal services that require generic DNS (with generic I mean name resolution besides SyncIQ target information; "outsider" names so to say) to be working initiated by the cluster?  All base configuration I had a look at, can easily be configured with IP addresses instead of DNS/names (i.e. smtp server, srs gateway, ntp server, etc.).
Dedicated "System AZ" groupnet without real DNS Server