It really depends on your airline's agreement with the other airline. If it's an ID90, the agent can choose not to accept the ticket, based on the argument that the prices can widely differ. If it's a ZED fare, as long as the mileage is within the same zone there's no reason for the agent to deny it. Same goes for service charge passes. In this case, IAH/TYS and DFW/TYS have only 10 air miles difference in routing, so there really shouldn't be a problem no matter what.