I was thinking some of the engine guys on here would have answered your good question by now. Cat got their fingers or writers block! So from the Village Idiot of Hemi:
The long rocker arm is on the exhaust side its not near the issue it would be if it was on the intake side. The exhaust rocker is aided in closing by the out going exhaust gasses. In a way, it has some help so the mass of the rocker on the exhaust side is not really an issue at all on the Hemi engines. It posses no problem what so ever to increasing the RPM range of the engine. Some Bob Glidden Pro Stock Ford Hemi engines turned well over 9500rpm with a similar length and far heavier weight rocker arm. We also have springs now days that handle much more than what we throw at them. The number one problem to increasing engine speed with a Super Stock Hemi is area. More precisely, valve area and port area. These engines are limited to a stock valve size and you can only fit so much air past a certain size valve.
