I'm the worst at tree ID but I don't think it's black locust. My side road is lined with them and the bark is substantially deeper on the trees of that size.. I'd take a picture but it's getting too dark..
I can't zoom in on the picture enough to see if it is oak (there should be medullary rays if it is oak), but it looks like Bur Oak to me. I don't see many Bur Oaks here in PA but it is common in MI I believe.
The pieces showing rotted heartwood really say willow. Oak tends to rot the sapwood first and locust just doesn't.
I don't have a guess. The bark looks too rough & deep for willow I'm familiar with. That don't mean much though, it's not birch LOL It's BTUs
White oaks can tend to be hollow at the base - some even large enough to fit Scotty Overkill inside! One of my biggest ones is hollow at the base too. I've never seen a black locust get hollowed out like that though. After thinking about it some more, I don't like it for BL anymore - the wood would appear almost green in a fresh cut tree. I don't like it for black willow either though. My book says they tend to be 'small' trees, and the bark doesn't quite match. I'm changing my guess to chestnut oak, which is a white. That's what I thought my BL trees were originally. A lot of homeowners can misidentify their own trees - I know I did. Even us wood obsessed guys can get it wrong. I say head over with there with the trailer and give er a big whiff. If it smells bad, maybe it is willow. If it smells like oak that looks like the mother lode!
I don't know, but if it has been growing in their yard, they should surely know if it is willow. There is a big difference between a willow and an oak when in leaf. The only willows I have ever seen are weeping willows, which, forgive me, I love.
