I posed this question on the macosx-talk list and got the following response from Ken Case of OmniGroup:
<<The fonts work fine in Cocoa applications, but you can't just switch to a symbol font, you need to actually enter Unicode characters which appear in those fonts.
What Mac OS X's glyph generator does is to look in the current font to see if it has a glyph corresponding to the requested Unicode character, and if it's not available in the current font then it searches through every other installed font to see if any of them have a glyph for that character. If it can't find any glyphs matching the requested character, it draws a special regional glyph which represents the general range of Unicode containing that character.
In other words, the user shouldn't have to select a particular font to get a particular character (and in fact that won't work), the glyph generator will automatically switch fonts to display the correct character as long as there's a font installed which can actually display it. If you want a particular symbol character, you need to actually enter the Unicode character for that symbol, and Unicode-savvy Mac OS X applications will automatically find the matching glyph in whatever fonts are available. (If multiple fonts can display the character, you could then select a particular font using the font panel.)
In OmniWeb, the easiest way to do this would be to use an HTML character entity, e.g. "α" for alpha, "β" for beta, etc. You can copy and paste the resulting characters into TextEdit, Mail, and other Cocoa applications, so it might be handy to find a web page listing tons the special characters and use that as a copy-and-paste source when you need a particular symbol. Alan Wood's Unicode Sample Pages (http://www.hclrss.demon.co.uk/unicode/unicode_samples_utf8.html
) might be one good source.
For more information on Unicode and Mac OS X, you might also check out Tom Gewecke's "Unleash Your Multilingual Mac" web site at http://hometown.aol.com/tg3907/mlingos9.html.
On that page is a pointer to the Code2000 font which has glyphs for 30,000 Unicode characters: if you install that font, you'll find that all those characters work in all Cocoa applications.
Hope this helps!>>
This is very different than what we are used to, but could be more logical if we are given decent tools for selecting the desired Unicode glyph.