The answer here is that anything can be used for masturbation, as long as it turns you on and pushes your buttons. Most devices sold as "massagers" can be and are used as vibrators for sexual stimulation. Massagers that would not be suitable for use on the genitals are those which are designed specifically for other parts of the anatomy, such as the feet or back. Percussive massagers for the back and shoulders aren't likely be effective tools for masturbation, but who knows? Different people enjoy different things.
Massagers tend to produce stronger vibrations, so if the sensation is too intense, you can place a towel between yourself and your massager, or use the massager through your clothes. Special attachments are available for the Hitachi Magic Wand that are designed specifically for genital stimulation, including attachments for vaginal or anal