RR,
I assume this process requires a fair bit of hydrogen, if they are converting (CHO)n into (CH2)n. Does the 40-60% less CO2 include the hydrogen generation, and how are they doing it?

The hydrogen may come from natural gas (that's the cheapest way to make it), although it could be produced from using part of the by-product fuel gas. Since propane is a by-product, it could be your hydrogen source.

In terms of energy input, it could be energy subsidized by producing hydrogen from renewable sources via electrolysis.

This would average down the EROEI on just pure electricity from the renewable, but if the resulting average is high enough and money can be made from it, I don't see why it wouldn't be worth doing.