那是允許的です。我は在寫する日語です。真的です。
It's like this one "Japanese" restaurant near my brother's place where everyone working there is Chinese, 80% of the customers are Chinese, and presumably if you actually asked them for Japanese food you couldn't get it.
But yeah, Japanese (i.e. the writing, not just romaji) is allowed, but I don't think you're allowed to abuse the privileged.