I'm a biy confused here .... maybe it's just the vocabulary ... but here's what it comes down to:
Is a motor overloads a load or a switch?
If they're switches, well, we put switches in series all the time - and there's no neutral wire. Just 'switched legs.'
If they're loads themselves, then putting them in series is a bad idea; code issues aside, Ohm's law tells us the voltage across each load will only be half of what it needs to be.
Putting the overloads in series seems to accomplish exactly the same thing you would accomplish by using an additional auxiliary contact on one of the starters - with the difference that now the two coils could be on different circuits, or different voltages.