This is why Ryan Hall is good for the UFC, he makes match ups like this VERY interesting. It'd be the same story with an Oliveira fight.
In this one I think Hall is a level above on the ground, Ryan's finished more traingles than TCity has had hot dinners. I think Hall would be confident working him over on the mat. Ortega's striking is better at the moment though, we'd have to see how well Ryan's striking develops but at the moment TCity has the edge.
If it went to the ground I could see Ryan eventually getting the tap, probably from a leg lock.