VMW goes up and Dell refuses to sell DVMT stock for the corresponding price?
Once a "tracking stock" is created; Dell doesn't control the price. It is determined by market. So once created, Dell doesn't have much say on the price.
Is there any guarantee that the tracking stock (DVMT in this case) will track the price of VMW, besides Dell's good word?
The guarantee is similar to other stocks. Dell or any other corporation will need to show separately the books for the "Tracking Stock". Technically it is the same as a separate company without the overhead of a legal entity. i.e. everything is kept segregated and dealing with other division are generally accepted cost models. So Dell can't show more debt on a "Tracking Stock" and shore up all profits outside of the division ... ofcourse Dell can still engage in some kind of frauds [similar to Enron, worldcom, etc] or fudge some entries to be advantageous to parent company. However in general the books are segregated and well maintained.
Incase of VMWare, its a separate entity on its own and Dell just holds defined number of shares, so it is relatively very easy to create and manage the "tracking stock"
There is a standard process of creating "Tracking shares" and extinguishing it. It follows the standard valuation process with disclosures to regulators [SEC, etc]. In case of Dell there is a move buy back the tracking share and extinguish them.