The Tado SRTs are only responsible for depressing or releasing the pin in the valves below them. They have nothing to do with the flow/return direction. That's down to the valves already fitted. So if your valves are fitted correctly now (or incorrectly) it will make no difference to Tado. It also shouldn't matter whether they are fitted to flow or return, so long as the valve is facing the right way. Bidirectional valves make the point moot.
However, if your existing valves are fitted incorrectly it is possible that Tado will open the valve just enough that the valve will hammer. I've faced this situation myself and had to swap the valve so that it matched the flow direction correctly.