With a 2200-2500mah Life on board, there's enough power available where you can darn near arc weld, so the addition of the ignition power to what's already going on not that big a deal at all (negligible).
When speaking NiMH, you need to be much more careful. Depending on what type and size servos you are using (std. analog vs. high powered digital) and the number of them you are using, you could already be borderline overloaded - prior to adding the load of the ignition.
With a module rated for 8.4v in hand, you can forget about the 4.8v suggestions regarding the older/original modules we had not too long ago. This fact should also help illustrate the fact that the equipment we are using is constantly evolving for the better (for the most part). This requires one to pay attention to when the information he is reading was actually written - in order to prevent getting bad/misleading advice.......