Welcome, scannerradio2001.
You can still monitor OKC on their VHF system. You can also monitor them on the new EDACS system, but most likely only for a short time. The new EDACS system is a ProVoice system, and you're right that scanners are not able to follow ProVoice traffic. They are simulcsasting their VHF traffic in analog right now, so if you plug those channels in, you should be able to monitor the talkgroups for now.
As for the issue of interoperability, that issue has been commented on several times in this forum. The new system will create basically the same situation we have now. To provide the ability for OCPD and OHP to talk, the dispatcher will have to "patch" the two systems together in specific events.
There is one possible caveat though. I heard an OHP officer on low band in OKC say that he was "...stopping by the city to get my new handheld programmed...". Since I heard him on low band, I know he was within a couple miles from me. Since he said "the city", and not "the radio shop", like they normally refer to their radio shop, I'm thinking he meant OKC's radio shop. It could be that he purchased an EDACS radio, or was issued one by OKC. It could also be that he was simply referring to his normal Motorola handheld being programmed by their radio shop.
I do know that he was here in OKC, and I know that it was going to be a short trip, because the other OHP unit that he was talking to was going to meet him for lunch afterwards. Interesting, huh?