HE (or she) who gets up early should also be accepted - "who gets up early" sounds incomplete in English.
There are some twisted common saying that we can funnily say:
Addig jár a korsó a kútra amíg el nem lopják.
Aki másnak vermet ás, az sírásó vagy földmunkás.
Jön még kutyára teherautó.
Kicsi a bors, de vannak barátai.
'Whoever' is a better pronoun than who here; who can be a relative pronoun or an interrogative, but is rarely the predicate.
I don't think "who" is the predicate here either, looks more like the subject to me.
"...aranyat lel" is the original phrase in hungarian, but if we are lazy or tired (in the morning) then we use the version "...álmos marad." It is a kind of funny modified phrase. :-)
I think ki (who) is interrogative. Am I correct? Should it be aki? No one else has commented on this. But I cannot see why I am wrong.
Yes, it could be "aki". Here, ki is a shortened form, because this is a (modified) saying.