In case anyone is interested, here's what I've discovered.
There are four font families installed with Adobe CS2 that don't remain in the Library/Application Support/Adobe/Fonts folder. They are Courier, Myriad, Symbol, and ZWAdobeF. All are PostScript (Type1) fonts—except for ZWAdobeF, which is TrueType.
Interestingly, these may be required fonts, but instead of remaining in the Requrd folder, they seem to be installed in the User font library. According to the Extensis publication Font Management in Mac OS X: Best Practices Guide (7th ed.), the font Myriad is required for CS2. Meanwhile, an Adobe forum posting by Dov Isaacs, an Adobe employee, indicates that ZWAdobeF is a special hack for Adobe Acrobat and serves a limited purpose but is best left untouched. The remaining fonts may or may not be crucial.
I'd lost track of the source of these fonts long ago and had no idea that they belonged to my Adobe applications. Although they'd remained in my User font library, several of them (Courier and Symbol) had recently been disabled—but not Myriad or ZWAdobeF. For the time being, I've decided to move them all back into the Requrd folder where they'll be activated for all relevant Adobe applications.
The Type 1 Myriad fonts are included for use by Illustrator.
We know what Symbol is but I have never heard of any Symbo font from us!
Oh, I just wrote down the file names as they appeared in the Finder.
Apparently, with PostScript fonts, there's always a Font Suitcase ("Symbol") that contains the "screen" information and then a corresponding PostScript Type 1 outline font ("Symbo") that contains the "print" information—so in this case, it's really just one Symbol font. The font suitcase file can contain the metrics for multiple fonts, which is why Courier and Myriad have 5 files representing 4 font styles (bold, italic, etc.).
I still wonder if Symbol and Courier are necessary and why—or if newer versions or different formats can substitute for the original Adobe versions. (My system fonts include a TrueType version of Symbol and a Datafork Truetype version of Courier; I don't know if these can be swapped out for the PostScript versions.) And I'm perplexed why the Extensis resource implies that Myriad is contained in the Requrd folder, when every other resource I've seen shows that folder as empty, except for the Base and CMaps folders.
In any case, I decided to go ahead and herd them all into that folder—partly to keep track of them and partly in the hopes that it might clear up occasional buggy application behavior. (Photoshop in particular has been quitting a lot, but that may just be CS2 and Snow Leopard not getting along.)
I was glad to find your posting on ZWAdobeF—it helped to put a few pieces together!