I own G-BZYD, ex army gazelle with up pointing exhaust (and SAS!). Water just drains straight through. All the rearward pointing ones cover the jetpipe when parked ourdoors but the upward pointing one doesn’t. No need, and no known problems.
And SAS is brilliant, I love it and find it a brilliant workload helper. Best tip is to keep it turned off during all take off and landings or it just acts as a nuisance.