I've seen it written that many chazzanim use "Adoshem" when singing (if not in the davening) as it has the same number of syllables as what they would be saying, namely Ado-noi, but that this is disrespectful, and they should just say "Hashem" instead.

Why is it disrespectful? Does everyone agree with this? What about using "Amonai" ("my Ammonites"?), as is done in the movie Ushpizin? I understand why it was done there (had to sound close to the real thing), but I've since heard a choir use it too.