Yes, reverse torque is important, particularly on the track.

IIRC I have heard that you can't use an ordinary bike powermeter backwards on the tandem because powermeters are set up to read zero when they see reverse power. For example if you freewheel down a hill then pedal backwards really fast you should see 5 or 10 Watts negative power. My bet is that you don't because it would look confusing so easier to drop the data.