Someone please correct me if I'm wrong but I've never heard of Kamikaze pilots being welded into their aircraft. You have to remember that not all pilots were able to complete their suicide missions. In describing the attacks on the American fleet of Okinawa in April of 1945, Russell Spurr mentioned that some of the suicide pilots (not involved with the fighter screen) needed to return to base due to mechanical problems. It would certainly have been more efficient to ensure that in such an event the pilot could be extracted and the aircraft repaired for a later attack.

If you expand you definition of Kamikaze pilots to include those in all "special attacks forces" including midget submarines then yes, some operators were locked in. Kaiten, or human torpedos, had cockpits that could not be unlocked from the inside. Should the attack fail, the pilot's only recourse was to self-destruct the machine.