It certainly seemed to work within the limits of what I could try. I started the tracker, left the phone in my car, and then did a shore dive. When I came back, I downloaded from my Perdix to the phone, viewed the dive and then hit the map icon (as you can see). You get this dialog. However, it did not find the existing site. I can only assume that's because from where I left the phone to where I have the dive site marked is probably 1/4 mile or more.
Anyhow, I'm sold even if just for marking sites. What I do now is take a GPX track, tag the photos I took on the dive with the GPX track, and then copy the location from the first photo to the dive site. This is like 10x easier.
Side note, it's interesting to see that the boat crew went back to shore when you are out diving...