Yes, but you'll want to put down PLENTY of bedding so that they can dig and scratch without having their instincts frustrated and you'll need to provide a dustbath since they won't be able to dig their own.
Access to natural ground is probably better, but one advantage of concrete is that it would be proof against digging predators.
Yes. LOTS of reasons not to, however. See above, there are things you can do to mitigate by essentially burying the concrete under new ground cover. I'd be more likely to move the dog cage (it if can be) to bare ground, and use the concrete pad for something else.
You can, but make sure they have plenty of sawdust or bedding over the concrete. Droppings stick to concrete, making cleaning up a nightmare!
(I speak from experience )
My actual chicken run is mostly concrete pavers which actually makes cleaning easier on me not to mention I don't miss the mud in there. I wouldn't go back to not having the pavers. But I have this in a fenced in garden area that I just leave the door open mostly and they free range that so they can scratch, forage, and play.
Part of my run is on concrete. I put lots of wood chips down. It gets nasty under there so make sure you can scrape it periodically. But as others have said it is far from ideal.