Lots of folks have made all heartwood unbacked yew bows. There's neolithic bows like that, see TBB volume 1 I think.
I bet maple would make a decent backing for yew. It definitely won't overpower it. Gordon made a really nice bamboo backed yew boo a while back. You could do a search for that.
I guess it kinda depends why you want to back it. If its because you just want to to make a laminate, well then go for it. But if its just for safety, you'd probably be fine with no backing, or just using silk or rawhide, or linen.
gr