Seems to me like it’s more of a wrapper for Python to communicate with actual Niagara emitters. Looking at the unreal engine files UpgradeNiagaraScriptResults.h and UpgradeNiagaraScriptResults.cpp, it looks like this class is what allows Python to safely access the information in the actual cpp class and read/write to it.
It looks like normally through Python you would use the basic Niagara Emitter class, and only use the NiagaraPythonEmitter if you are trying to read this specific information. However, there is nothing in the Unreal Python API about this class, so I am unsure how to actually access an instance of it. Perhaps you need to get your regular emitter and cast it to a python emitter? But this can be done in Blueprints, so it makes no sense for it to be called a Python emitter.
Sorry to leave you with more questions than answers, but hopefully a kind soul will hop in to shed some light on this.