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.
".. 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)
1984 Fast/Nicholson 345 "FastForward"