This may be a stupid question but how is that different than the auto SPN generation done by the NAV installer? We started those steps yesterday and when I did the setspn -A ...., it told me I was going to create a duplicate SPN and it ended the process, so from what I can see, the SPNs are already setup.
Also, if the SPNs were not setup, wouldn't the web client fail for all users, not just those on 1 domain?