I feed raw and kibble together and have done so for about a year now without problems. I know they say it digests at different rates, but I can't see why that should be a problem. If dogs were still scavenging, which is what their system is adapted to do, then they would eat stuff all day long that digests at different rates.
We humans also eat stuff together that digests at different rates and I can't remember ever having had a problem because of it.
I haven't actually ever found an answer why the different digestion rates should be an issue...
So if it has never caused a problem to feed it together, I can't see any reason why you shouldn't!
Vera