Well, you have to keep in mind that Animorphs is an entirely sci-fi series, whereas when you start having re-animated corpses, things start straying into supernatural territory. So all bets are off, really.
It's pretty much impossible, even theoretically, to keep a brain alive without a heartbeat. The brain requires oxygen to function and think, which requires blood, which requires a heartbeat. Even if you could use the Force to somehow animate the rest of your body without metabolism happening, your brain is still the part of you that controls your use of the Force, ergo, if it dies the whole thing falls apart. Another possible explanation, however, is that his brain is not the source of his consciousness, but rather he possesses some kind of 'collective consciousness' comprised of the midi-chlorians in his blood.
So, supposing that his brain is somehow impossibly still alive although the rest of him is dead: the Yeerk could control his brain, and, assuming a Yeerk could make use of his powers (a question we can't really answer), the Yeerk could animate his body, same as he could.
Assuming, alternately, that his brain is dead too and his consciousness is spread out through his midi-chlorians: you'd have the same scenario as the Hawjabrans, a bunch of tiny brains spread throughout the body. Thus, control would not be possible.
