Oh heck. Mac is out 24/7. Sometimes his back is wet when I go to get him. I dry him as much as I can with a towel, put on a wool saddle pad and ride him. The saddle gets rained on . I get rained on. Mac gets rained on. We get back, I towel dry the saddle, put it in my car (it will mold if I leave it in the barn), towel Mac , feed him some hay and put him back to be rained on somemore.
Some of the horses get rain rot if left unblanketed. So, they are dry when it comes time to tack up, which is a great convenience. When done, however, I have to be sure they are mostly dry before reblanketing (rain sheet is what it is, really).