I used to have a charger and a seperate 3.5mm jack in my honda for my ipod. It caused a lot of interference and made a whirring noise when the ipod was charging and playing music at the same time.
If that adaptor you posted doesn't incorporate controlling the ipod from the headunit/elsewhere, i wouldn't do it. Head units that are ipod ready are cheap, and a lot safer than searching for music on that little click wheel... I had to do that today in my car and it sucked compared to the deck I have in my jeep.
If you want, with an aftermarket deck you could easily just run the USB to that hole you have there by removing the bolts on the climate controls and then popping out the cubby/heated seats with a putty knife.
Not to poop on your thread, but I think it'd be more cost effective and would give better sound if you just went with an aftermarket deck.
01' Silverstone WJ Limited
-Debadged, K&N CAI, Quad taillight mod, Yellowtop Optima, 3000 watt stereo setup, Kolak 3' Catback (flowmaster 70 with magnaflow tip and high flow magnaflow cat) with DMH electric cutout, Overland woodgrain wheel