You don't have to use the ECU. Yes, the axles have to be modified but it looks pretty easy. Here are some good write-ups:
E-locker
Retrofit Electric Locker
Toyota Electric Locker
One of these write-ups is a retrofit into a Tacoma. If I was installing it into a model that came with the factory elocker as an option then I would go with the ECU controller. Otherwise, I don't think that it will add anything.