But does Temper stack with equipment/job traits?

If so, I cannot see a problem with 5% rate.

DA Khanda +2 = 10%
Atheling Mantle = +3%
Brutal Earring = +5%
Calmecac Trousers = +3%

RDM already has 20% in respectable equipment DA.

Potentially 30% if one opts to /WAR for the job trait (arguably not).

With DA Khanda +2 being upgradable in the next update for more DA, Temper's 5% put's RDM closer to the 50% cap and is quite respectable.