^Vero never looked Caucasian to me personally, closer to Asian or latino, though Italian fits well too especially with his name sounding vaguely Italianish. Black hair + light/fair skin is usually used for Asian human characters in anime with black hair being a common phenotype among italians/latinos so that's probably why.
Anyhoo I've went over this in my head many times and I won't lie in that it kind of affected my player choice in playthroughs. Since there's 6 trainers I'll give them multiple ones.
For Vero: as people have stated,this guy looks like he grew up in Reborn's dirty southside ghetto and has that street vibe about him. I feel his starter should sort of reflect this, being something with attitude and muscle yet still having a streetwise sense to it. Personally I'd go with Chimchar since it turns into Infernape that emphasizes a hard hitting and fast offense but it also a trickster in its own right. Squirtle is a nice pick as well since wartortle's bad attitude and Blastoise's cannons fit his street vibe well. I'd even give Tepig a shot here too, as while it's not clever looking in any sense it certainly looks the part of a brute that would be fitting. Plus its ears resembles a bandanna.
Alice comes off as the most feminine and ladylike of the PCs, also seeming more shy than the others. Chikorita would be my immediate pick for her, with fennekin coming second. Charmander could work too actually, as I like the contrast of "the maiden and her dragon." dynamic. Alice seems like she'd have a thing for fairy tales too which Charizard looks like he came straight out of.
Kuro seems rather laidback and more of a brains over brawn kind of guy, as well as a quick thinker. Froakie like many others have said seems like a great match for him, but I'd throw in Treecko as well. Turtwig seems rather chill too so I can see it fitting Kuro.
Lucia would be the Genki girl of the group; fun loving, energetic, and a bit quirky as well. I like the idea of her having Mudkip, totodile or Torchic.
Ari seems like the quiet loner of the group, but one who would favor strong pokemon with an intimidating presence. Bulbasaur, oshawott and Cyndaquil would be my picks for xyr if mainly because their evolved forms having that vibe to them while their base forms seem a bit more solitary..
Decibel to me always looked like xe came from Lapis ward or an upper class background as opposed to Vero the hoodrat, even having this bit of noble confidence about xyr. Piplup, Snivy, or Chespin would fit perfectly.
How Alola's starters would fit is up in the air since we don't know what they'd turn into. Going by base forms alone, I'd give Rowlette to Alice or Decibel, Litten to Vero or Ari, and Popplio to Lucia.