Heller was even with the same squadron 488-th, but he was assigned to it on 21-st of May 1944 so a few months after the collision - see below (on a side note, check the last name in the list of the assigned on that day! This is the name that inspired him for Yossarian. ):I remember reading somewhere that this mid-air collision was likely what inspired Nately and Dobbs' deaths in Catch-22, though I don't remember where I saw it. It's been a while since I read Patricia Chapman's book on the 340th BG and how they inspired Heller's characters. Not sure if he was with the group at that point. Speaking of which, I do recommend the book.
Heller uses the mission on Sept. 23, 1944 (when 488-th and 489-th BS bombed the cruiser "Taranto" in La Spezia) for the deaths of Dobbs and Nately, but it's quite possible that he learned about the mid-air collision in the squadron or even studied it in detail after the war.
Copied from "Historical Sources for the Events in Joseph Heller's Novel, Catch-22" by Daniel Setzer
Cheers!