I would be surprised if the engine would you in the tilted position, unless its a "happymax" with fuel injection. The risk is getting water into the cylinders through the exhaust ports or valves which would cause a hydraulic lock and serious damage.
Whilst you can't flush an outboard kept on a mooring at least the water pump will be emersed so salt crystals won't build up in it. Worth regularly checking the anodes though to make sure they are disolving nicely, because if they are not then something else is
Pete