Weyland's A.N. says, amongst other things: "Search R&D for 1 card and add it to HQ."

Meanwhile, Weyland's agenda Project Atlas has a hosted agenda counter mechanic, and it reads: "Search R&D for 1 card, reveal it, and add it to HQ."

Is this an oversight, or does this imply that Aggressive Negotiation allows you to covertly add a card from your R&D into your HQ?

It does mean that Aggressive Negotiation lets you add a card from R&D to HQ without showing it to the runner. For the same reason, if you chose a face-down card to retrieve from your Archives with Archived Memories, you wouldn't have to reveal it either (a face-up card would be already known to the runner).