Autoglass have told me Direct Line automatically refuse OEM glass. I've told them fine, but I will be inspecting the glass before anything is fitted. It needs to match the climate comfort spec (acoustic, solar blue, etc) and ideally be a brand I've heard of.
The woman at Autoglass was helpful, and I did ask her (thinking of this thread) what insurers tend to approve OEM glass, and she said Liverpool Victoria are usually fine with it... not that we often have much of a choice when it comes to insurance in this market.
Edit :: Oh, and Autoglass did give me the option of paying an additional amount for OEM, but it was £900, so not exactly cheap...
Why not go with them in the future?