This is one thing for all of the pairs of genuine friends doing this, but I also have two friends who I introduced to each other exactly once, and who have never spoken since, who have a 6 year snap streak together, and both of whom have streaks like that with dozens of other people, many of whom are virtually strangers.
For the two friends I'm thinking of, my impression is that they don't know each other any better through snapchat than they do from me knowing both of them and mentioning them to each other (they live 1000 miles apart and only met once). I guess the best I can say is that I would be comfortable seating them at the same table at my hypothetical wedding. Same vibe as my cousin I have on Facebook but have only really met twice in the last decade.