I understand that clients roaming between Ap's should be a seamless process, however is that also true if a client roams from the 2.4ghz radio on one AP to the 5ghz radio on another AP? (same SSID).
Seamless roaming only works when you enable 802.11r/k/v on the AP's and on the clients. Most 5Ghz networks use more than 20Mhz wide channels (eg 40, 80 or even 160 in bad designed networks) and 2.GHz only 2.4Ghz so this is already an issue. And if you are using 802.11ac then only the 5Ghz is supported. 802.11n is the highest standard supporting 2.4Ghz. So roaming will work but it wont be seamless as there are 2 many variables different. I suggest you use 5Ghz only as 2.4Ghz is crowded anyway.
Theory vs reality is quite different with 2.4 + 5ghz roaming. I'd side on creating an independent 2.4 network at specific locations only if you need legacy devices on your array. Having a combined 2.4+5 SSID network should allow all clients to pick the fastest/best one but what one will find is that either a client will stick to 2.4 because the RSSI is good despite the band being crowded with traffic/slow, or the client will jump to 5ghz in the not most seamless way causing user frustration since it'll either drop a video call or cause a hiccup.
