Is a pulse width modulating thermostat compatible with a W2 auxillary heating (Nest compatibility question)
It looks like this type of heat is called "modulating heat" or a "modulating furnace".  I can't find any information saying that Nest supports that.  

The labels on the thermostat and furnace are meant to be a convenience for the installer, and you really have to refer to the equipment documentation to see what it does. The common labels of R, G, Y, W, C are fairly standard, but once you go beyond that, there are conventions, but you have to research to know the exact use of R, W2, B, etc.

That's a long way of saying that just because the furnace happens to have a W2 label and the Nest also has a W2 label doesn't mean very much.  You have to dig into the documentation (as you have done).