The scraper and a tray do basicly the same job. The scraper is better at removing the oil clinging to the crank. Your talking .060" clearance to rotating parts vs inches. The tray can't get close enough to do that. The tray does keep the rotating oil and crank action from upsetting the oil in the pan. Heck I use a hand fitted scraper, directional screen in the pan, multiple baffles, trap doors, and a swinging pick up.
Doug