I have tanked several of the Nightmare bosses on my Vanguard alt. I've never worried about my DPS. If you are hitting enrage, (a mechanical enrage in this case), either your DPS is low, or something about your strat has reduced your time on target. Looking to tanks for DPS always seems a little suspect, though I do understand that in this case it's a proactive tank looking to push his group over the top.
That being said, anything you can do to increase your DPS without losing mitigation is great. It's when people start to actually lose mitigation that I start to raise my eyebrows.
The only thing i can always contorl is my own acting. So i try to find out the limits of my playing with help of the comunity. It is much compfortable discussing playstile or tactiks in team, than doing it on my own. Also thanks for the other two hints improving our dps.