They seem to understand each other's peeps and chirruping noises. The chick is robust enough, and mom seems careful not to tread on it. If the chick is well-mothered and survives, chalk another one up for interspecies bonding.
I have a second turkey hen sat on four eggs -
Well, technically, she's sat on a blind chicken that's sat on four eggs but the 'Mom Sandwich' (pat pending) is keeping the eggs warm and the hens happy, so again I'll let it play out. Nature always knows better than me.