The thing you must remember is having the monk as offtank he is not getting hit 90% of the time thus he is not building up veng. As such even if he performs his rotation perfectly he will have a fraction of the dmg he normally has when tanking due to missing all that veng! Thus even a non perfect dps spec / rotation / gear should outperform a tank than is veng starved!
BrM gear should work perfectly for WW too, unless you're reforging avoidance and ignoring hit/exp for some awful reason. I don't know about Guardians; last I looked they reforged dodge on everything.