Devery Jacobs, who auditioned for Dani, answered a fan question on Twitter about Blu where she talked about more about being in touch with your Native heritage vs the color of your skin. So if Blu only began to claim native status in order to audition for Dani, then yeah, big no.
https://twitter.com/danimoonstarr/with_replies
I think that's more of the right mindset we should approach for her.
Roberto on the other hand has had a history of being lightwashed in the comics, which has been rightfully critiqued. He's mixed in the comics, since his mother is a white Brazilian, but the comics clearly originally depicted him as Afro-Brazilian. Zaga is Latino and Brazilian yeah, but it does show Hollywood's preference towards lighter skinned POC. (Like Zoe Saldana being cast as Nina Simone)