According to the comprehensive rules, the definition of shuffling is thus:
701.16a To shuffle a library or a face-down pile of cards, randomize the cards within it so that no player knows their order.
If you use a proxy (an honest, third party entity) to search your deck for a desired card (let's say you used Demonic Tutor), then when the proxy has located and presented you with the card, you still have no knowledge of the order of the cards. [note 1]
Since as far as you or your opponent(s) know, the deck is entirely randomized, is it necessary to go through the act of physically moving cards around? It seems that it already meets the requirements of a randomized deck. Sure, the cards are in the same order as they were before, but since there was no prior knowledge, there is no present knowledge. [note 2]
Is it strictly necessary to go through the physical process of shuffling if you use a proxy to dig through your deck?
note 1: This assumes there were no previous 'place on top of your library' or similar effects.
note 2: This assumes your proxy will yield no information or provide assistance based on the knowledge gained by looking in your deck.