It was actually a pretty good one, I think. Having him join a small nomadic group and live with that group for awhile before "discovering" ASZ. That way he showed up surrounded by people who were convincingly innocent, because they WERE innocent, making him much less suspicious. It also helps explain why Michonne et al, whose guard is way up right now, were fooled here.

However, it introduces another problem. When they discovered Dante was a mole, they should have immediately also suspected the other people he came in with.

Anyway, this helps the timeline add up. Gabe said Dante had only been at ASZ for 4 months, which I at first thought was an error in dialogue, since Alpha sent him shortly after the barn scene, which was closer to a year ago based on Coco's age. But then while watching Dante's ASZ intro tape, Dante states he was with that little group for "a few months", so it basically adds up.