Are the wireless users dropped onto the same subnet when they go from building A to building B ? If you use the same subnet then it should work. Is the problem that when the client goes from building A to B, that they have to hit a portal page and enter their username / password again?
Probably don't need mobility enabled, could use availability instead, since you only have 2 controlers. Mobility is if you have more than 2 controllers, or if you are using routed topologies. In your case you have 2 controllers and you are using bridge at controller.
Are you using nac?
inter-area - you can draw the Area on the OneView map. When the client enters there it will send VSA back to NAC, so different Role can be applied.
Default setting is none by the way for mac-based authorization on roam. You would enalble for the visibility.