Thank you Chris and Alex for your input.

I would just use two battery packs, i have to on Apex as i run 14s on the weapon and either 6s or 12s on drive (ive used ampflows and brushless on drive), I wouldn't recommend using the same battery pack for drive and the weapon, especially with the current draw the LEM will take.
Ideally yes, I would prefer running the two circuits separately but I cannot reconcile that and the fact that rule 7.5 of the FRA build rules states that for either LiFe or LiPo, the maximum number of cells in series is 12. Does that rule only therefore apply to a single battery pack or does that apply to the whole robot (the latter being my interpretation at the moment)?

I would also like to add you absolutely CANNOT run ESC's in series like that. Labelling them as a variable resistor is far too oversimplifying of what's going on inside them. To also add if it were the case the voltage would be split by how loaded the motors/ESC's are, it wouldn't always be a neat 50:50 split and would likely overvolt the ESC's extremely often in the course of a fight.
I used the label of variable resistor as I couldn't think of a better way to describe the way in which it worked at 4am in the morning :P I do recognise that it is a gross oversimplification to label ESCs as such.

I don't claim to be an expert in electrics (my background is computer sciences) but it was my understanding that the voltage seen by each component in a circuit was the total voltage of the circuit as supplied by the batteries divided by the number of components in said circuit, least to the ESCs themselves. I can see how the motors running would potentially affect the amount of current each ESC receives, I suppose that would be the same for voltage as well but I don't see how that would lead to one of the ESCs overvolting.