Is it fair to use real people in poems or fiction? Strictly speaking, it’s probably not. But the people in poems and stories are never “real.” Even in memoir, they’re re-imagined and re-purposed.
This leaves them in an interesting spot. Charles Foster Kane is not William Randolph Hearst—not exactly. The Charles Lindberg in The Plot Against America is not really Charles Lindberg. Richard III is not Richard III. Consider this hypothetical: I make a friend of a bad-ass death metal guitarist who happens to also have a non-ironic tattoo of a little kitty cat. I decide to incorporate these two contrasting details into a novel in a character who shares no other characteristics with my friend. Still, my new friend quite reasonably believes himself reproduced in the book, and if the character is evil or stupid or perverted, my friend will justifiably object. I think the only answer, really, is to write the best books and poems you can, try to write what’s true—even in a fictional context, especially in a fictional context—and go to bed at night dreaming about what you’ll write tomorrow.