Recently I was forwarded a clip recorded at a well known Shi'i conference in the United States.

In it there is a speaker (unidentified) who puts forth claims that all Prophets would say "Ya Ali". This includes Prophet Adam and Prophet Ibrahim, and even goes on to say Imam Ali and his assassin said it as well. I've attached the link to the video below.

Now I understand the importance that has been placed on Tawassul in Quran and ahadith, but Ive never come across something like this. Maybe this is due to my own ignorance.

So are the claims provided by this speaker valid or found in Shia literature? If so and they are authenticated, what would be the reasoning?

I was there and saw this as well. The person is a famous poet. The part about about the prophets seeking help via Ahl ul Bayt (as) is true and I have done a lecture about this as well.

However the part about the assassination is just him being poetic acting as if this would have happened, yet it has no record in the history.