I would not count on it.  Why not install and additional access point to your network and extend your wifi coverage?  I’ve done so in my Garden for the same reasons you have.

I don’t think the Sonos Roam (or Move) will be used across SonosNet connections either, simply because they are intended as portable/moveable products and so would be "making & breaking" the SonosNet Mesh signal as the player was being moved around the Home. That could cause a lot of issues.

I would personally opt for installing a wireless mesh network system in the home instead, just for the portable products and other Home devices to use …and I would then go onto see if all Sonos devices run well on the WiFi mesh setup. If they don’t work as before, I would resort to cabling one Sonos product to the primary Mesh Hub/Router device and then run all non-portable Sonos products on SonosNet alongside the Mesh WiFi system… that would be my personal choice, rather than using access points, which might be the cheaper option, and of course could work too in some cases, but they are not a Sonos supported option, whereas a WiFi Mesh system is shown in the system requirements as fully supported (see footnotes at below link)…

https://support.sonos.com/s/article/126

I just think a WiFi mesh setup would bring added benefit and network coverage to the whole of the Home and possibly the garden areas too.

Access points are supported. It’s extenders which are not. 

The simplest option would be to get a few cheap access points, and wire them to suitable nearby SonosNet nodes. Assign them all a separate SSID from the main router’s, to stop any other devices casually piggybacking onto the SonosNet backhaul. Configure the new credentials into Sonos. Powercycle the Move or Roam and it should find a nearby access point.