From what I gathered, i would doubt they knew each other personally, but by reputation i would believe so. They all made their bones at Loum onward...unless you look at the Origin AU lol then Char made his bones in the Dawn Rebellion lol.
As for wanting proof...how about some tell him since he has the drop on them and if we do anything stupid were toast...how about he come out of his mobile suit and show his face...since Mott (if i read ZRC's post here right) and Gray would be huge scholars of the Great War, I would assume they've seen his face in the archives and that alone will scare the living shit out of them for seeing a living ghost...followed by the immediately begging him for an autograph XD (unlikely to be immediate given the situation but before they part company with Norris some will want an autograph from him XD)
- - - Updated - - -
And that right there folks shows how green Gray is-
Notices the Sheppard bit...IC what you did there XD