Well, if a Russian knows French more or less and sees "Юго" he might pronounce it rather close to French - that is without [й] sound at the beginning but it won't be [у] either (I might be confusing something but I think I heard it in some French films). If one sees "Уго" I think it would be more difficult to guess. Anyway, if it helps, there are Russian last names for which it's not evident for Russian native speakers how to stress them correctly - so the way words are written is not always sufficient for them to be pronounced correctly.