Same question posed to Foreflight support confirms the wifi connection is one at a time. You can connect to Skyview or you can connect to your Stratus Adsb wifi receiver, but not both at same time.
It's what I expected, since each is acting as a wifi access point, but it does point out a drawback of this type of expansion architecture, where every peripheral wants to be the iPad's sole access point. Would have been nice if it could be the other way around, where iPad's hotspot feature is used to connect to it. More a critique of Ipad than Skyview/Stratus, I suppose.