Unless you have a balanced rudder that takes very little force to move, a pendulum servo vane will struggle to sail with wheel steering. If the steering has few turns lock to lock, it will take lots of force from the vane to move the wheel. The vane may not generate enough power to move the wheel especially in lighter winds with low boat speed. If the wheel has lots of mechanical advantage but many turns lock to lock, the vane won't be able to turn the wheel far enough to get enough rudder movement to effectively steer the boat. On my boat, the Monitor wouldn't steer the boat under 4 knots. The vane rudder just didn't develop enough force to turn the wheel without more boat speed. Strangely, even though the boat developed a pretty fierce weather helm and needed a lot of force on the wheel as boat speed picked up, the Monitor would steer the boat okay once boat speed got above 4 knots The vane didn't work at all connected directly to a stub tiller. Even though it wasn't steering through the wheel, the vane still had to move the cables and spin the wheel for no purpose. There was just too much inertia/friction in the steering to overcome. Having said the above, many boats report good performance with a servo-pendulum vane attached to a wheel even on boats as large as 50'. Assume they had a balanced rudder that took little force to turn and steering with very little friction/inertia.

I think a pendulum servo vane would work best with hydraulic steering and the vane attached to it's own tiller. You'd have to have a pressure relief valve/disconnect on the hydraulic steering so you didn't have to fight the hydraulic pressure in the ram but that's an easy fix. A system set up like that would have no/minimal drag from the hydraulic steering and the vane would give full travel to the rudder. The best of all possible worlds.