I think it could go either way, really. For example, (using Angel Sanctuary as my example, as it has many different spellings as well) the katakana for Rosiel (or Rociel, though I much prefer Rosiel, honestly) is 'Ro-shi-e-ru', and the katakana for Raziel is 'Ra-ji-e-ru' (if memory serves me. I'm in Toronto and my manga is back in St. John's. ^^;; lol) Both use the 'shi'/'ji' sound to represent 'si'/'zi'. I guess it's up to preference until Hoshino comes out with an official spelling. Hell, even with the official spellings I still use 'Theodore' if only because 'Theodore' makes far more sense than 'Tiedoll'. Not to mention both would have the same katakana, technically speaking. Same with Crowley. ^__^; Also the fact katakana implies a foreign name/word.