I suspect I might answer my own question, but here goes.

I have a Goodwe ES inverter. Most of the house is backed up. What isn't backed up is the sub DB - out buildings (including laundry), pool pump, 2nd geyser.

Now, if it's a nice sunny day and there's no load shedding, I can run all of this stuff off of PV. If there's no load shedding it still runs, but if there's insufficient PV it will draw from the battery. 

So the inverter is rated at 4.6kW. When there's lots of PV, the pool pump (for example) is running off of inverted PV power. But when there's insufficient PV it will start drawing from the battery. 

So does the pool pump's 750W count towards the 4.6kW limit? I suspect that it must (whilst there is grid) because the DC comes out of the batteries, gets inverter and generally goes through the same circuitry as the backed up loads. So what about when there IS sufficient PV? There must still be some inverting going on to produce the AC that the pump requires.

So I guess the question really is whether or not those non-backed up loads are part of the 4.6kW limit?

My DB board is split into what the electrician called essential and non essential loads.  I suspect your backed up loads = essentail.  I think you did indeed answered you own question to check if its part of the essential (back up) loads turn off grid power and see if you can still power the pool pump.  If you can its on the backup load. The risk as you would know is that if the pump turns on during load shedding and there is insufficient solar it could drain your battery.