This reminds me of something Bruce Lee said in an interview regarding all human beings having 2 arms and 2 legs, so movements will be similar regardless of what martial art one is doing as long as they are trying to achieve a similar objective from a particular principle of movement. I tihnk this sort of helped his idea of having no structure as structure.
In studying a bit of Taiji Qin Na I have found some very similar movements to Aikido's kansetsu waza (joint technique) mainly. Of course my Taiji instructor said the Aikido movements I was doing were the same as Taijiquan and he also indicated that there was some historical link between the Chinese arts and Aikido. The same thing happened when I studied Qi Gong under a Chinese master. When I showed him some of my Aikido he said, Aikido is Qi Gong.
On the reverse side I have attended a Shaolin Qin Na workshop and at one point the guy proceeded to show a variation of Rear Naked Stranglehold Tenkai Kotehineri (Sankyo) with an atemi to the groin and called it an "Aikido" technique. Again, this was an attempt to show the "common foundations" of the different arts.
On another note, the Judo principles used for kuzushi and many of the throws are the same for many Aikido technique, except that the distance used is different.
Personally, I have gone from believing there is a historical Chinese link between all of these arts (even going wayyy back to the study of Aiki In Yo Ho by the Aizu monks and its roots in Taoism and Tai Chi), to seeing it as common principles expressed via a common medium of expression. If the human body is supposed to apply circles and straight lines to achieve certain tactical advantages in unarmed combat, then because of the similarities in the concepts/principles used and the general sameness of the medium involved (i.e. the human body in a vertical plane), there will be overlap.
But this is because of the limitations of the human body and the similarity in principles. Its sort of why a bubble is spherical in shape and so is a planet. The same laws of physics (generally) apply to both things, with the spherical shape being the most efficient form to be used to achieve a similar purpose. Martial arts are also based on the principles of efficiency in achieveing certain tactical objectives in combat.
Its the same way we see similarities in Graeco-Roman wrestling, Judo, BJJ and other forms of floor grappling. Similar principles, same medium of expression.
Just my thoughts on the thing.