You could use one or the other, your choice.

Also, binding Tenebrous (which is not optional for an Apostate) qualifies you for the Turn Undead requirement, so you can take Tenebrous Apostate as a single-class Binder (oddly enough). This also means (for you) that you only need one level of Ur-Priest, not two, if you don't want.

Of course, having the daily uses of Turn Undead has its own advantages which may make it worthwhile. I would think that Tenebrous's Turn Undead would not qualify for Divine Feats.