Well is it good ukemi to be running and "sliding into home plate" before nage even does the technique? The guy wont let you get kuzushi because he is running into you and sliding. Literally. I have never seen anyone do that before. This guy is throwing himself with no help on my part...much to my annoyance. I can't wait for some high ranking visiting Sensei to ask him "What are you doing?"
Actually, it's not a bad way to practice if you're careful with it. You get end-to-end control over the ukemi without anyone pushing on you, then you can move up to having someone apply pressure (ie, the throw) while still keeping control over the ukemi yourself. Basically speaking, you always want to maintain as much control over yourself as you can - even when you're falling.