This is a simple and elegant fix, and I think it unifies our wiki's identity well.
One challenge though: it assumes the admin will always control their domain. What happens if the domain expires? I've had friends who have let that happen, someone else swoops in to buy it (hijack it), and they're forced to either submit to extortion or just abandon the domain.
If everything is forwarded, then the only way to manage the site is via the private domain. And if the private domain goes, so goes the wiki's admin control. Is there a simple way to forward all categories except admin?
It can't be a common problem, and I suppose it's also possible to contact the Wikidot team and ask for some administrative help. But you might want to spell that out.