Very nice engines (the Hanno is one of my all time favorites)! Yes, that carb on the RFP is for in flight mixture control. Seems a bit unnecessary on a pumped engine. I have thousands of flight on my Hannos (I keep a log) and the high speed needle rarely needs adjustment; only when there is significant atmospheric change. That looks like a two nipple pump on the RFP which is not original. The original had 4 nipples: fuel inlet from tank; fuel return to tank; fuel outlet to carb; fuel return from carb. Is the mixture control carb an OS carb? Or aftermarket? It looks very well made.
What airplanes are they going in?