Well I could concede that sabbath is somewhere in between, they've done a fair lot of stuff that is definitely not metal, songs like 'air dance'
And then you've got bands like deep purple, definitely rock rather than metal, kinda blues-rock mixture if anything, like steppenwolf for another example, rock-blues fusion.
Metal, I'd categorize bands like say, mudvayne, five finger death punch, disturbed, tesseract, as metal, without being rock. With something like papa roach as somewhere in between.