You are free to write the aliases of your voicebank OTO using any characters in Shift-JIS, such as English letters without accent marks, numbers, and Japanese characters. Because Vocaloid's English phonemes are based on SAMPA, you should be able to write all of the letters and symbols in an OTO. As long as the lyrics in a UST match the aliases in the OTO, it will be able to use that voicebank's samples.