As Carol-san mentioned, most JA hams surprise when DX station send Japanese in ROMAJI (alphabet) since they(we) are not familiar with decoding Japanese expressed by ROMAJI.
And as Thomas-san said, there is Jpanaese Morse Code (WABUN). Most JA hams learn and use WABUN Morse Code when they want to converse in Japanaese language. ?
I learnt WABUN code when I was 17 (45 years ago) to get 1st class ham license.
(Both International Morsecode and Wabun Morse Code proficiency were requested at that days)
As Izumi-san, OHA is nice way to shorten OHAYOU which everyone can understand, but sometimes rude for eldery person.
In this case, OHAYOU GOZAIMASU is better ? It becomes too long and too complicated hihi.