I have never heard of someone doing this, does not sound like a good idea.
Probably the problem with the washing machine is if the water is too hot.
I rinse my tack off with a water hose and soap to clean it thoroughly and then let it dry well and oil it. Never had any trouble.
I don't think that's a good idea, water is the leather's enemy... You should use a glycerine soap after after nourishing with an adapted oil :)
I've never tried it but that definitely sounds like a bad idea