I don't see the problem... current is current... wether it goes to a servo or a plug makes no difference to the battery. And because of the high voltage (4.8V) the current is only a few hundred mA at the most (starting)... and even much less at anything above idle.

These units have a built in voltage cut off: if the battery voltage drops below 4.8V when the glow power is active the power to the plugs gets cut off.
They also have a built in battery monitor: you can tell the condition of your (receiver)battery from the indication led... killing two birds in one stone (or dollar )

And anyway, if you are really worried about it you can always supply the glow current from a separate battery.