For Toneri and Hamura,they awakened the Tenseigan,which did allow them to use the TSB,but the Tenseigan allows you to use all 5 elements and Deva Path (similar to the Rinnegan) and the special Chakra Mode (similar to the Sage Mode)..so yeah..they were also both aliens,if that matters to anyone..
Asura was a direct descendant of the Sage and did not even need any Uchiha powers to use the TSB,so i don't know..But the Sage "blessed him with his power (Six Paths Chakra) and made him the successor to Ninshū." so i think that had something to do with it.
I mean,anyone can use whatever they want i guess,it's just that i don't see this as being a Sage Mode only thing because you either need access to all the 5 elements (Rinnegan/Tenseigan) or the Sage's chakra,which i don't see being just Uchiha + Senju,because like i said, Madara did not have anything similar to Naruto or Sasuke powers after meeting the sage.
Finally,i would also like to add this,"By drawing on the power of the tailed beasts, Naruto enters a second state and dons something similar in appearance to his Tailed Beast Mode cloak.This second state granted Truth-Seeking Balls, further enhanced Naruto's abilities and his Tailed Beast Mode avatar " and "Jin no Sho does not state whether the chakra of the tailed beasts is a component of the Six Paths Sage Mode, but the chakra is stated as such in Shikamaru Hiden: A Cloud Drifting in Silent Darkness. It is not known if this was a mistake from the novel."
But like i said,do what you want,i just wanted to add my opinion for the TSB since i was not active during that time and people were talking a bit about it here.