I did a couple of hazel/yew bows about a year ago, and was very impressed with the combo. One was 120lb with an almost dead flat hazel back, and went off to a customer who I think is still shooting it on and off. The other was lighter, about 80lb I think and was a spliced yew belly with highly crowned hazel back. I was experimenting with tied on nocks at the time and ballsed it up twice so ended up scrapping the bow but it was fine until then! I didn't heat treat the belly, but the yew was exceptional - the really tight, dark English stuff that starts to look like teak with some oil and sunlight!
I was quite reluctant to let the heavy one go as it shot better than a similar bow with a yew belly from the same tree and an elm backing which surprised me.
On both bows I kept the belly fairly rounded but not quite as round as the typical Victorian D section. I trapped the back much like you do with a heavy yew warbow, leaving quite a narrow strip of the hazel running down the back but I would imagine it would work just as well with a more modern/Victorian laminate style with full width backing.
