This is going to be controversial, but I don't think Whitebeard needs to be a Buccaneer.
I'm not trying to disparage or deny the theories/parallels; I respect and acknowledge those possibilities.
1) Newgate was always portrayed as an orphan who essentially started from nothing and worked his way up, becoming immensely strong to protect those he cared about. His origins and dream to have a family are quite humble and make him more relatable to the audience. It's incredible that he has the second highest bounty of any pirate so far and yet was never interested in the One Piece in contrast with his peers.
2) Oda pays special attention to body proportion when designing characters. WB is one of the very few, especially of his size, to be well-proportioned. It makes it more akin to him just being an oversized human than from a specific race. This fact also extends to his crew members and their designs, some of which are enormous but share a similarity with this theme. Is Oda going to have every human 3 meters and above be a Buccaneer? What does that tell us about some Wano characters like Ashura Doji?
3) Buccaneers are a persecuted and nearly extinct race. Yes, WB was about 25 years older than Kuma, so the timeline does check out for him having some connection with his unknown parents. However, there is no information available on whether Newgate had a known bounty in his early days of piracy prior to joining the Rocks Pirates. Neither is there any evidence of being having Buccaneer genes in his blood, though that may be revealed by Miss Buckin during her MADs days. WB was seemingly chilling during his younger days just as much as Teach remained in the shadows with no bounty.
4) Every emperor has been special in some way: Shanks is a mystery with possible connections to underworld or world nobles, Big Mom being huge as a child compared to her parents is not explained, and the same goes for Kaido’s race. Luffy is the sun god, Blackbeard has a strange body, and Buggy is a whole other story.
Does WB need to be special in this case? He already had all three haki and obtained a supreme-grade blade, and there’s the devil fruit on top of that. He's got enough going for him already; does he really need to be part of this near-extinct race? Sort of rubs the wrong way for some reason.