Surely you wouldn't actually tell passengers the broken down units were slowploughs, and they would fall into one of two categories.
The first is the average traveller who will hear an announcement about a broken down train. They won't know it's a snowplough because they weren't told it was a snowplough.
The second is someone with a keener interest in trains, such as us on here, who would seek information out on what train had broken down, and find out it's a snowplough. I would hope that most in this category would be able to work out that units like this often need moving for operational reasons outwith actually being used for ploughing, such as maintenance.
I therefore see no real value in actually telling passengers it was a snowplough. If you tell passengers it was a snowplough you'd probably have to tell them why the snowplough was moving in August, and suddenly it's an unnecessarily long announcement and things to tell passengers when they ask.