I've done it, pretty stupid, but it works. you need enough speed to get up the ramp, then you can't stop.
This is how i do it all the time. No issues, load it by myself all the time.
This works well.
The best way is not to "beef cake" it up the ramp. you have more of a chance to screwing it up just like the DA in the OP. With the engine and some decent throttle/clutch control, it's easy to do this way. I do it the same way all the time and even without the steps to get into the bed. (i'm 6'5 so i can just step up into the bed.)
I've even done it without a ramp - i had someone hold the rear while i dead lifted the front wheel onto the tailgate, then i had a friend hold the front wheel while i squatted the rear end up and walked forward until the tire could push onto the tailgate = that shit was hard!