Neville:
Thanks for your well thought out response. A few comments, if I might.
First of all, the puzzle you're thinking of was the Tue 4 Jan 2005 NYT puzzle by John Underwood (aren't search engines wonderful?). Thanks for the chance to see another example of a scatter theme.
Second, I rechecked, and the Susan Harrington Smith puzzle I noted does not seem to mention the theme anywhere in the clues. Perhaps there was some kind of external clue. But I think I could argue that my theme would be easier to figure out than hers, since I would make reference to it several times in the clues.
EX: This composer penned nine symphonies, all of them famous [BEETHOVEN]
Here, the fact that Ludwig von Beethoven wrote nine symphonies is fairly well known, and therefore useful to the solver. I agree that all clues won't be quite as helpful, but others would be, like an INSECT having six legs (fairly common knowledge, I think).
Of course, the best way to see if this would fly would be to submit one of these puzzles to an editor and see if (a) the puzzle is rejected completely, (b) the puzzle is accepted but an explicit statement of the theme is added, or (c) the puzzle is published with no explicit mention of the theme. If I get to that point, I'll be happy to share my results here.
Peace.
---Todd
P.S.: Good luck with your rebus theme!