I have the holster/case combo that I purchased in one of the Verizon stores. It's the same one as seen in this review:
Review: Verizon Shell/Holster Combo case for the Motorola Droid 2
I recently bought the commuter case from Otterbox and while it's tight, it does fit in that holster. My Otterbox case makes some weird "snapping" noises when you squeeze it and putting it into the holster definitely squeezes it. Sounds like I'm breaking something every time I slide it in the holster.