Not going to happen, Its been going on for decades regardless if the district/school is union or non union. This happens with all positions not just coaching.
With that said, there are a lot of headaches and other essential duties that come with being the head coach or lead that many general instructional or support staff or administrators do not want to assume at a school. (Even though Admin has to be at the games anyhow).
There are also a lot of coaches that do not have principle or administrator credentialing that actually impact a building more so than the building administrators. Coach Parker at WW was a great example of this and there are many more around the area as well.
A lot of these guys and ladies have supplemental contracts for weight room monitor, lunch room monitor, study hall monitor, facilities and grounds etc. to try to sweeten the pot for a coach they want to keep or get. If current staff want to apply most schools allow them to do so but their contract may also state they are already responsible for some of these duties. Some teachers may be dismissed without any formal interview while others may decide to de select or go through the process knowing they would most likely not be selected.