- When Treetop Village comes back under your control, will it be a Zombie?
- If you animate it using its ability, will it then be a Zombie?
And to clarify a possible confusion: Yes, Treetop Village will return under your control with a +1/+1 counter on it if it died as a creature (under your opponent's control) even though it will not be a creature when it does so (it will be simply an unanimated Treetop Village.) Grave Betrayal's triggered ability only cares what it was when on the battlefield, not what it becomes once it hits the graveyard.
The answer to the first question is simple: As long as Treetop Village is not a creature, it simply cannot have a creature subtype (this is specifically stated in the rules of the game) and therefore it won't be a Zombie.
The second question is a bit more complicated.
Another clarification is needed at this point to avoid confusion: Yes, the effect of Grave Betrayal will be constantly applying to Treetop Village for as long as the latter is on the battlefield, regardless of whether it actually causes a change or not. It not being a creature does not cause the effect to cease to exist. (It just means that the effect isn't actually making it a Zombie if it's not a creature.)
Also note that "it's still a land" really means "in addition to its other types", which in turn means that its effect making it an Ape creature does not overwrite any other types or subtypes it may have.
So, if Treetop Village becomes a creature (eg. by using its own ability), does it become a Zombie? If you answer yes, then you haven't been reading this blog enough, because it's not that simple...
This is a rather peculiar case where the timestamps of effects have a non-trivial consequence.
There are now two effects affecting Treetop Village (on the same layer): The effect that says it's a Zombie, and the effect that says it's an Ape creature. The former has an older timestamp and is therefore applied first.
And that's the crucial point: Such effects on the same layer are evaluated one by one, in timestamp order (unless they are dependent effects, and these two are not.) This means that "is a Zombie" is evaluated first, but at this stage Treetop Village is not a creature, so that effect does nothing. Then we evaluate the "is an Ape creature" which makes it a creature (of subtype Ape.)
This means that it will be an Ape creature, but not a Zombie.