The example in the KDX User's Guide shows the TOC greyed out, i.e. unavailable, and it isn't mentioned in the text either. So it seems likely that the TOC isn't available. This is very surprising, because, as cmumford says, PDF TOCs are typically well supported.
PDF TOCs display ok with the Sony ebook Library software, so I assume they are included in mobile Adobe Digital Editions. So this seems to be another example of the rushed job that Amazon has done with PDFs.