Correct! In English a word-for-word translation makes it sound as if "Bändi is a Sami person." I am only saying that the English sounds odd. I am not saying the Finnish should be reworded, but I am saying that the English could be since languages never translate very well word for word or sentence for sentence in a natural way.
I get a comment about using the accent on the 'a' in Sami; however a special 'a-accent' is not provided on the screen, unlike for umlauts on 'a' and 'o', and I have no idea how to type an 'a-accent' on an English keyboard. It would be helpful to provide the letter when it is going to be needed otherwise I simply cannot type it.
"Band" is a collective noun. Whether it takes a singular or plural form of verb depends on the emphasis. "The band are Sami" stresses the fact that there a number of different people in the band who are all Sami. Yes it is correct English however such constructions are more common in British English than US English.