The use of the check valve there is a nifty idea and theoretically should minimize the risk of a flooded exhaust (from cranking too long without firing, eg) getting into the engine.. but I suspect, as Denise suggested, that it became a trouble spot more often than it prevented a problem.
I'd venture to say that most systems will not have one in place and as long as you follow good practice you could eliminate it now.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)