It is a particular class of passive, a "Pasiva refleja" (This is difficult, even for natives)
Yes and not. The English grammar is different to the Spanish grammar. I think the categorie of you sentence (in Spanish"pasiva refleja", but not "pasiva")does not exist in English grammar. It's a mixture from "English pasive" and "English unpersonal"
Is not the "pure passive". In a passive sentence, the subject receives the action (and the verb is expressed like passive)
Passive. "El mar es visto por alguien" The subject (el mar) receives the action (es visto = he is seen).
In your sentence, "el mar" is not the subject.
So, "Se ve el mar" is a "pasiva refleja. Not a passive sentence, not a unpersonal sentence.
(It's difficult, it's for an advenced level)