I was not aware that the drives themselves had a seawater intake. Perhaps they do; I just haven't had occasion to work with them much.
The intakes for the engines and other systems on a boat should be checked regularly for fouling and such. If you don't do it at the end of a trip, you get to do it before the next trip, which may cause delay, or you get to do it during the next trip, which may be a career decision....
I know the noise of an Arneson drive is similar to that of a helicopter, but to compare level of maintenance..
We had a trial on a yacht equipped with such a drive once. Didn't look at this area of the construction much, but i suppose the engine requieres cooling so checking if the duct is clean is a good practice. Should always be done if a posisblillity of serious fouling exist.
I have driven a couple of boats with arnesons and neither of them had sea water intakes for the drives just the regular intakes for the engines. However the props themselves were very susceptible to any marine growth and needed to be cleaned regularly or boat speed would suffer badly.