Unfortunately you probably did piss away that money due to marketing and internet forums. Catch cans, while they do something, don't really do anything to prevent valve buildup in DI engines. I've posted it on here before, there was an actual independent engineering test/study done and the empirical evidence shows blow-by is not the source of valve deposits. It's primarily due to exhaust gas reversion caused by the variable valve timing which is done to create EGR flow to improve emissions. This happens mostly at light load and with cooler engine temps (aka short trips). Your fire suppression guy is hauling ass on the highway all the time, so he's not operating in that condition most of the time.
Yes, a catch can does stop some amount of oil mixed with a larger amount of water vapor, but it won't affect the formation of valve deposits to any real degree. Having said that, I won't tell anyone not to use a can. If it makes you feel better to use one, by all means use one. It can't hurt... unless you forget to empty it and the engine sucks in a big enough slug of water.