It looks like the paragraph Palm is referencing can be found towards the top of the second page of the USB-IF Membership Application, specifically this sentence:
Unauthorized use of assigned or unassigned USB Vendor ID Numbers and associated Product ID Numbers are strictly
Although, at the same time, the way Palm restored iTunes syncing with the Pre was to have it use Apple's Vendor ID Number, which is also expressly prohibited by another couple of sentences in the very same paragraph:
Each Vendor ID Number is assigned to one company for its sole and exclusive use, along with associated Product ID Numbers. They may not be sold, transferred, or used by others, directly or indirectly, except in special circumstances and then only upon prior written approval by USB-IF.
So unless Palm has already acquired said written approval from the USB-IF, they are also in violation of their agreement.
It looks to me like Palm is very clearly in the wrong, and that Apple may or may not be, depending on who gets to be the official interpreter of the phrase "unauthorized use." I have to say, in a world where "ID" is normally short for "identification," using a "Vendor ID Number" to identify devices that came from that vendor sounds pretty standard.