Peter, wet sumping hasn't really been an issue on modern engines since the 1970's. My BSA Rocket Goldstar used to suffer from this but not any Harley I've owned and the S&S is a similar type of set- up to the Harley.
You can get a non return valve for the oil feed line (a lot of people fitted these on British bikes, not me though) these, if they seize up or block will obviously starve the engine of oil - Not something to look forward to.
On the English engines sumping would come to light when the bike was kicked over and it dumped it's now siphoned black load all over the block paving. - Trust me her who is really the boss went absolutely ballistic -
I guess running it regularly is the answer.
