On my 05 I had to reroute the rear speed sensor wires to the ZFE and have the bike reprogrammed.
I think some others have piped around the servo but left the servo module in place. As long as the servo is still connected and doesn't have an electronic fault in it's processor (unlikely IMO) the speedo would still work. Not really sure about the newer non-servo bikes though.
"You can follow me, but it's gonna hurt"