I’m trying to install the Red series switch for a 3-way switched fixture that doesn’t appear to be on the same neutral as the switch. There is a neutral in the same box as the primary switch since it supplies an adjacent outlet. Can I use this as the source of neutral even though it doesn’t continue on the the light? I can’t locate where the neutral for the actual light is sourced - it’s coming in from a separate location and has the black wire clipped off.
Here’s what I’ve been able to put together:
That would be strange if it wasn’t on the same neutral. Can you ohm it out at the light fixture and first box? It are there other lights inline?
That is bizarre 
My guess the installer didn’t have a 3 wire cable so they hacked it.
I think you are asking about putting the dimmer in the box one the left side of your dwg. Yes you can. The neutral really doesn’t have anything directly to do with the power to the lamp. The Dimmer neutral simply powers the dimmer radio and control logic, and perhaps the LEDs.
BTW your current wiring will not pass any electrical inspector’s review.