Actually, I've been heavily researching this and here is the info I've managed to sqeeze out of the Dell customer service reps (after several calls and many hours and days later).
1. Ownership is transferable for monitors. And with ownership comes the right to any valid warranties.
HOWEVER:
2. Ownership can ONLY be transferred if you have all of the correct information of the person who originally purchased the monitor from Dell. That includes the original Dell order number and the name, address, phone number and email address of the individual at the original time of purchase from Dell.
3. If any one of those pieces of information is in incorrect, they will not let you transfer ownership. So if you have the correct order number and the correct name but the incorrect address, they won't let you transfer it.
4. You cannot transfer ownership via their website because the website transfer form is only for products that have service tags or express service codes, and monitors don't have service tags nor express service codes. So instead you have to call Customer "Care" to transfer ownership.
SO, to really purchase a Dell monitor on e-bay and make sure you can get the warranty/ownership transferred, the seller has to be willing to give you all their personal information so that you can call Dell to verify that their information is correct before you buy the monitor. But you will be hard-pressed to find someone that trusting, because as soon as you have all their info, and have verified that it matches Dell's record when you call, you have the power to transfer ownership through Dell right then and there, even if you haven't purchased the product yet!
My own story: I purchased a brand new Dell monitor from ebay that is a 2005 model theoretically covered under a 3 year warranty. A whole line of pixels went bad recently. If Dell would only look at my monitor they could easily verify that it is a 2005 model, which means that I still have about 2 years left on the warranty. It has a valid serial number but they don't use serial numbers to verify authenticity of their products for redemption of warranty services (so they tell me). Since, when I purchase the monitor, I did not know that I needed to transfer ownership and since I can no longer make contact with the ebay seller to get all of his original information (he's no longer a seller), I'm stuck with a bad monitor. Dell won't even let me pay them to refurbish it!
Bottom line. Dell makes it really hard for you to buy second hand products and still use their warranty because they want to make more money by pretty much forcing you to have no alternative but to buy directly from them. They don't put any of the important information on their website because they don't want you to know it. It's taken me a week, with many hours of being on hold and being transferred around a lot just to get my questions answered. This is hard-earned knowledge, so spread it around