I think you're wrong, man. At the very least, I think you're making an Uneducated Guess. Heh.
The NCAA Bylaws are the "rules" we're talking about, particularly Article 11, "Conduct and Employment of Athletics Personnel."
I just read it through in its entirety. There seems to be no prohibition to Gruden's ESPN employment and his UT employment overlapping, as long as it is properly reported and documented.
Here's one applicable section of Article 11:
So not only can Jon Gruden be employed by ESPN (TV or radio program), he can also continue to endorse Hooters, Corona, and other business enterprises, as long as he notifies the University of those obligations and they are consistent with UT's policies concerning outside employment. Note that the University reportedly does not approve of the Hooters or Corona links, because they don't want scantily clad (orange and white clad, no less) women and alcohol to be directly connected to UT's image. But that's between UT and Gruden; the NCAA by-law does not prohibit it.
This element of Article 11 specifically allows Gruden to be paid for work outside of UT:
Here's the one element of the By-Laws that may require coordination between UT and the NCAA. It does not explicitly address TV reporting, is geared toward print media, but the spirit of the rule may require coordination:
Other than that, I see nothing that would in any way apply to Gruden working for ESPN for a few more weeks.
So, UneducatedGuess, what rule book were you talking about?