Hosing down any really hot metal can cause it to warp or crack, but give the brakes a few minutes to cool and then hosing them is no problem. They get hosed all the time when you drive in the rain, though puddles, or whatever.
Squeals and squawks, though not there by design, are certainly common enough. What you heard in reverse may have ben the slack adjsuters, which try to automatically make adjustments in the brake mechanism for better braking. The slack adjusters can get rusty from lack of use and squawk loudly if you brake fairly sharply in reverse. Do it several more times and it should clear up and also improve brake performance.
Squeals going forward may be dust, dirt, rust, etc. Go Rving more and see if it gets better.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL