Literally debuts in ninja gaiden as a ninja who "chose the path of the ninja," dresses like a ninja, fights with ninjutsu and lives in a ninja village.
If that doesn't count as a ninja, I'd be very curious to hear what the criteria for being counted as a ninja is.
The one shown above was made by the Freiza Force for Freiza's soldiers.
Bulma later made several suits based on the Freiza Force's armor designs.
Allegedly, they can stretch to "any size," hence why Vegeta was able to turn into his Great Ape form and still wear his costume as if it fit. Though...