In my experience as a VT homeowner we have relatively frequent short outages. It's pretty rural and the weather is brutal. I think the grid doesn't have as much redundancy as denser areas. We had one 3 day outage 2 years ago in the middle of winter which got quite dangerous, but otherwise I haven't had anything more than a few hours.
Also we have propane heat - but I need electricity for the blower and control board. So the electric consumption is pretty minimal, but it is critical.
Assuming they set up the house to island, which depends a lot on the install. Otherwise live power from a house in an outage is a big risk to those working on solving the outage.
Most are hours but there are enough that are a day or more that it is a valid consideration. As to when, honestly I think there are more not snow related. Long stretches of wet (or floods) and high winds not a good mix.
You also need to take into account the fact that VPP systems like this stabilize the grid by flattening the peaks and troughs, and reduce the average length of outages.
> around 50% of the houses in its programme with home batteries also have solar panels
I'm assuming most of these outages are from snow storms. Do these people have to go up on the roof and clear the solar panels?