Go to a scav lobby -> create group -> invite somebody
Open the log checker, select your latest log file, and it will tell you if they have an rare items in their inventory.
Not sure why BSG sends and logs all of this data locally, but, its all there and you can just manually check it yourself.
** This does NOT work if the person is already in your group. You have to invite them at the Lobby screen because I am lazy and didn't want to make checks for both **