Vandy, you asked about the holster, not the case. and the holster for the innocase works with the tpu cases and others as well. Though, I did some arguing with Seidio, and they sent me the updated version and gave me a $20 credit. The updated case is a much firmer fit. I'd still like it thinner, but it's still on par thickness wise with the tpu cases. So I've gone back to the innocase.
And no, the amzer and other tpu cases are not thinner than the innocase. They are about the same. Both fit in the holster and proclip holder without making an adjustment.