And the other safety was... Darian Stewart! Not Mike Edwards as expected. Very deep dive add. Played in the box some too, but not as much as Whitehead.
Another deep-dive safety add is a guy playing mostly linebacker: Raven Greene of Green Bay.
Based on snap alignments, it looks like a lot of defensive backfields came out sitting back a bit, including teams that like to play a safety forward, like the Colts, 49ers, Bears, and Packers. Perhaps that evolves as DCs have 2019 tape with which to game plan. I did, however, read over the summer that the 49ers would do more to disguise coverages with their safeties rather than have Jaquiski Tartt come forward so often. Even so, I didn't expect an even split of box safety snaps between Tartt and Tarvarius Moore, of all people. It seems the box safety is going the way of the fullback. I've begun to look for guys playing slot snaps as well for matchup-based starting line-up decisions.
Answering a previous question, yes, A Harris and T Walker are generally playing deeper while H Smith and Q Diggs move around more. Walker did see some slot snaps.