Speedo is only part of the problem. If the speedo is 'proofed, but the water gets into the motor, it will interfere with the sensors and give you problems. The main reason to run sensorless is to avoid that problem.
I recall that people running old-style GM speedos (early ones built for s'less only) and motors managed to run s'less without problems, but don't know any certain combinations of sensored that will work sensorless. It's a shame that most Section Rules no longer quote the BR motor lists - the best answer for a wet car is to run BR! HTH
