Is it in line with the pali cannon suttas to accept other scriptures? According to the suttas 


Are human beings capable of discerning what dhamma is outside of the suttas?

Is it possible to know enough from the suttas and then make use of the Abhidhamma?

What about the mere possibility that a dhamma practitioner could make use of Jesus's teachings, Hindu teachings, Sufi teachings or sutras outside the the official Theravada context?

When is it appropriate to be more closed minded?

When is it appropriate to be more open minded?
Other teachers do not teach all four types of clinging;


  
  Clinging to sensuality
  Clinging to rites and rituals
  Clinging to views
  Clinging to a doctrine of self
  


https://www.accesstoinsight.org/lib/authors/nanamoli/wheel390.html

Only Buddhadhamma is for the abandonment of all four. Other teachings in as far as they include abandonment of a type of clinging are to that extent wise.

Brahmajala sutta explains various wrong views and speculative doctrines about the world which are basis for other religions.

Also when hearing or reading teachings it should be compared to teachings known to be true, to see if they align and if they do they align they then ought to be accepted. I think this is in the great references sutta.

Making use of Abhidhamma depends on what you want with it. It's quite useful for improving expression and understanding of the Dhamma as it breaks down many teachings word for word, it will improve understanding of terms like jhana, factors of enlightenment etc. In this sense it is very useful imo.


  Are human beings capable of discerning what dhamma is outside of the suttas?


That's a mark of a Sotapanna in this sense; In the Sarakaani Sutta Buddha says that if trees could discern what is rightly spoken he would proclaim them a Sotapanna how much more so his son Sarakaani who took to drink https://www.accesstoinsight.org/tipitaka/sn/sn55/sn55.024.wlsh.html