In Access Recruit, whilst it's not currently possible to assign multiple hiring managers to the same position, you can chose one and and setup a delegation group for the other. To do this, follow the steps below.
Create a delegation group
Click Config then click User Groups.
Click +New then enter a name for the group.
From the Group type drop-down menu, select Delegation.
Under Granting Users, select both of the hiring managers.
Under Receiving Users, select both of the hiring managers.
Click Create User group.