IMO i think it's enough too - a special case is just when you setup a new appliance where the shipped packages will be from the community repo and even though you supplied the userdata for the supported repo it will not be downgraded during grommunio-setup.
Especially if you first run a grommunio-update from cli or cui and then run the setup.
If you don't it will probably not be that dramatic w/o it and a direct grommunio-setup as that will first add the repos and then the (hopefully at this time) version on the appliance build will be lower than the current supported gromox version.
And of course for all other packages aswell from that repo.
