Make sure you use a relay with the float switches, even though the pump may be rated below the amperage max of the switch, the start up current can fuse the reeds together and you get a freshwater flood into your sump or tank.
Can you give us some details on how the relay needs to be wired? I am in the process of seeting up a ATO as well and have not seen anything showing a relay and agree it makes sense to do so.