Asking if rdm could DD and tank at the same time is a question that is obvious to any rdm who has tanked in the past, and therefore an invitation to trolling :p. However I will try and answer with some dignity.
They don't give efficient hate. There's one guy on bg who claims he's able to build hate with a combination of full blown spamming of hojo/kuryami/jubaku, plus cure cheating; but even if it is possible:
1) it will become harder to do as level cap increase because curing will generate lower and lower levels of hate as dd do higher and higher levels of dmg.
2) eliminates anything that was useful about rdm gear wise in the first place since you have to fulltime full haste/enmity/fastcast gear; you can no longer fulltime terra's staff, nor refresh gear, or any other form of dmg mitigation really.
I responded why he was wrong, he told me no he did it and it was possible and pretty much the thread went dead again at that point.
Even with +30 enmity ichi spam will barely outweigh shadow loss from a slow attacking mob. Cures are only way to generate ce beyond that, and are not mp efficient, nor effective at all really. Once you start taking dmg, theres really no realistic way of saying you can maintain ce with cures and ichi spam alone. If you take minimal dmg during a fight maybe, but otherwise..
Your time would be better served trying to solo nms with that ninja sub, or leveling a dd or tank job to 80.