Why does everyone seem so fixated these days on Fast/Seamless roaming?  I've yet to see an example of an application that _requires_ fast roaming to work.  Folks have been using basic roaming for the past 15 years without issues for >95% of all Wifi applications.

That said, to answer your question:

If I recall correctly, the only way to have have different SSIDs on different AP's in Omada/SDN is to create multiple sites, adopt different subsets of AP's into each of the sites (each individual AP can only be a member of one site, as I recall).  And then create different WLAN profiles for each site -- some of which may have duplicated SSID configs (in the case where you want two sites/sets of AP's to offer the same SSIDs and some of which will have their own unique SSIDs instead or in addition.

To that end, I would expect that the ability to perform Fast roaming across multiple AP's would be constrained to only those AP's which share a WLAN configuration within one site.  I would not expect Fast roaming to work across Sites -- this would not make sense -- as a "Site" could be a geographically separate location.  I would expect each WLAN profile in each site to have it's own separate "encryption salt".  But it's possible I could be wrong.

But, basic roaming should work fine.  Basic roaming is when two more AP's are configured to use the same SSID, encryption method (e.g. WPA2-PSK-AES), and password.  Basic roaming works across AP's of different manufacturers and even different networks.  Basic roaming will work fine in the example you gave and it's what STA's have been doing for 15+ years before Fast roaming became a more common feature of 802.11ac (aka Wifi 5) networks.

-Jonathan