How is that patently untrue? Even a so called "clean" colony will have parasites of some description. Certain parasites will possibly be in even higher numbers than for the same species living a feral existance through no other reason than the constant contact and higher density of animals in close proximity.
The important part is whether those parasites are worth worrying about and can be passed on to your animals.
Will a feeder have parasites? Almost certainly.
Will it cause any harm to your animal?
Depends on the parasite. As you noted many are species specific or need another intermediate host or set of circumstances to complete the cycle but at the end of the day the feeder still has parasites.
Just not ones you need to worry about.
The important part is whether those parasites are worth worrying about and can be passed on to your animals.
Will a feeder have parasites? Almost certainly.
Will it cause any harm to your animal?
Depends on the parasite. As you noted many are species specific or need another intermediate host or set of circumstances to complete the cycle but at the end of the day the feeder still has parasites.
Just not ones you need to worry about.