playframework/Play20 — comment on commit ee7f22a146558a502b111cc78bd3b777f6a89a6e
File:  line 0
By pk11:

If you disable the plugin, then onStop/onStart won't execute, so the de-registration should not cause any trouble (the assumption is that registration happens on onStart, de-registration on onStop but because you did not use the plugin to create the pool, the registration did not happen onStart, hence your issue).

That said, we are working on making the DB plugin more abstract, so you will be able to plugin your implementation and use it as play.api.DB