OK. I went ahead and installed the Sprint Zone app to check this out. It isn't installed by default with the Blue Kingdom Rom. The rom removes most of the stock apps, which is what I wanted and why I chose it over the forgotten kingdom one.
nick8278 if you are interested on your end in checking it out, if you google com.sprint.zone.apk, you can find it on some of the android forums. I can't post a link yet, otherwise I'd post it here.
I can verify, for anyone else on Sprint, that once installed you can go to:
Help>My Device
--and there see that 4G indeed connects when it is toggled on, in a 4G wimax area.
Within the Rom itself you won't see the 4G mac address show, or get the 4G icon up top....but it does successfully connect and use 4g wimax.
And yes, thanks jssa28 for a great rom in blue kingdom. It's the best ICS rom, at least in my opinion, for this phone I've come across.
Also thanks patsfann for pointing out the Sprint Zone app.