I think it's possible that Irving Berlin might have met Scott Joplin. Berlin was apparently closely associated with Snyder Music early in his career. I think he was working for them as a copy editor or something when they started publishing his early pieces. During the same couple of years that Seminary Music was Joplin's publisher. I'm guessing they must have at least bumped into each other because Seminary and Snyder shared the same office space at that time.
I only met his daughter briefly but I thought she was quite nice. Must have been back in 1994 my wife got a last minute call to fill in a short slot on a tv talk show with some piano playing when, purely by chance, we met her sitting in the waiting room about to be interviewed on her new book. So I chatted it up with her while Sue belted out "I Love a Piano" as kind of an impromptu intro for her. We thought she was such a warm and effusive personality, we kept the car service waiting while we stuck around to watch her interview which was quite fascinating, focusing almost entirely on the personal aspects of their family life. Which, due to his super-star and her mother's elite-family status, sounded like it spawned religious and class-related controversies similar in their fervor to those surrounding the late MJ a century later... must be an occupational hazard.