It seems that if one looks hard enough, one can find quite a bit of historical reading regarding Ueshiba and some of his students being pushed.
Tenry pushed Ueshiba (don't have link handy)
Ueshiba's students pushing on him (multiple links, but I really like this one: http://www.aikidojournal.com/?id=1145
It's in the comment from Ellis about Terry Dobson.)
Tohei being pushed.
Shioda being pushed. (Can find only one link right now. http://www.budovideos.com/shop/custo....php?pageid=10
Tomiki is pushed. (Ellis has posts on this here at AikiWeb.)
There really isn't any doubt that Ueshiba and some of his early students used pushing as a way of determining a level of skill.
But, wait, it seems that the Chinese do the very same thing. What, you say? Why, yes, the use nearly the very same tests.
There are many, many examples of Chinese martial artists using a push to determine skill level.
What, then, are the differences? We know there are (Even the Chinese have a variety of ways of doing push hands.) Is it just a matter of individual application of Internal Skill? Or is there really a completely different internal skill in Ueshiba's aikido? One that requires a different training regimen to build? (Some of the basics have to be the same, though.)