[Mythor]

Given that this is really a mod that's mostly going to be seen/used by moderators/admin and that that page is the only place his copyright notice appears, I see absolutely no problem with it. It's not anymore intrusive than any of the dozens of other mods that do in fact put links in the footer or elsewhere - including vbSEO which you have to pay for.
The mod does exactly what it says on the box with a minimum of fuss. Two links back to vbulletin.org - not his own personal sites - is an exceedingly small price to pay for such convenience.

(note: the name of the site in my sig is a coincedence, I don't know the developer at all, just use his mod. )