HiGeoff:
This may be a little dated for your question but thought I would share my experience. I've been running 2 Airport Expresses and 1 Apple TV for some years now and they have been solid performers. However, about 6 months ago I decided to install a Google WiFi mesh network with 3 base units, Gigabit WiFi sounded like a good idea to me. Anyway, I had the same question, will my airport express stations work with the Google WiFi. Nobody seemed to know. So after a 3 month wait for the Google gear it came, I unplugged the Airports and setup the Google WiFi. It was too easy. Once everything settled down and synced up with the mesh network. So, I noticed that the Apple TV hooked itself up to the mesh without any bidding from me, nice. So, I plugged the Airports back in and let the mesh do its thing, after a while the Google magic worked and the Airports were online. Sure makes streaming from the iTunes store pleasant.
So, I just upgraded the firmware on the airports via the mesh and it all went quick and clean, no fuss no muss. Yea, tech that works, I love it.
Mochenpa