- I couldn't find the word subtitler in most English dictionaries.
- Most spellchecker programs underline subtitler.
- An internal search of threads at UsingEnglish for subtitler used to produce no matches (before this very one post).
No, there isn't, because you can't find it in the dictionary. (Note the way we often say the dictionary, as if Oxford, Merriam-Webster and all the others were all part of a lexicographical equivalent to the Bible).
Don't despair. Hollywood knew what best boys and gaffers were for years before dictionaries got around to telling the rest of us.