The salt and moisture are definitely what will kill the dump valve/components more than anything in a daily driver application. I have one on the exhaust of one of my trucks and at the moment it's completely ceased up after only a couple of winters post install. Of course higher quality components will ''typically'' stand up noticeably better and if you take the time to clean and lubricate things now and then you'll likely avoid the same trouble that I've experienced.
I've never ran one on my Subaru's, but I know Dustin H. had one on his JDM SF Forester and Geoff R. had one on his 2012 Sti. I believe they both ran them right off of the DP. They're both Saskatoon boys that I think you've met and I believe they're both still in the local FB group. That being said Dustin (Sask08STi on here) is likely the better one to inquire with as Geoff never has a car long enough to offfer feedback for situations like this.