You don't buff reaper and make it unused at arena because of many reason:
Grabed open
No damage
Short stealth time
And ...
Any way,
If it is possible please check reaper's skill "soul spike" as super armor work correctly or not? Because the other players could use their unsuper armor skills during reaper's "soul spike" is running.(no knock down effect)
It's normal or there is a bug?
I could send you many videos.