He seems to be romanized “Arty” on most other Pokemon sites. “Properly” romanizing his name アーティ would result in “Aati”. I think it’s supposed to be English-y and “Arty” is more correct.
If they use katakana for his name, then you're more than likely correct since most times katakana is primarily used for non-Japanese names. "Arty" is probably the right way to go.
