Nakisa, I took the class that Donna teaches online and we spent one class discussing POV in PB biographies. Some notes from that class:
Most are in traditional 3rd person POV Close with past tense.
Some unusual POV formats are:
3rd person/present tense: Malia- Activist for Girls Education
1st person/past tense: I am Jane Goodall
1st person/Direct Address: Blockhead, The Life of Fibionocci
3rd POV using real character as lens: The Extraordinary Mark Twain - According to Susie
Invented 1st POV: Voice of Freedom by Fannie Lou Hamer
Fictional POV Character as Lens: Abraham Lincoln Comes Home
2nd Person POV: The Iridescence of Birds. Jesse Owens, Fastest Man Alive
Direct Address Narrator/Alternating Tense: Houdini- World's Greatest Mystery and Escape King. I Dissent. Who Says Women Can't Be Doctors?
I may have some of these titles wrong. Just reading my chicken scratch. But Donna does an excellent online class and I think she's open for registration right now.
Also, as you probably already guessed, some of these in 1st Person POV or who use fictional characters to tell the story are blurring the line between NF and fiction. Melissa Stewart has many Twitter conversations about what can be accurately called NF. I would check out her blog, Celebrate Science, as she has many posts that talk about NF writing in general, not just science.
Other authors that do a lot of PB bios, like Candace Fleming and Barbara Rosenstock, may have some posts about POV in bios. I don't know for certain if they do, but I have taken classes from Candace Fleming and she is passionate about biogrpahies.
I hope this helps.