I'm just guessing here... but AFAIK, DomU is contained except for the device I/O and other calls to the hypervisor (or in your case since you're using Windows, the hardware extensions and then the hypervisor) being contained means it can't be accessed directly through Dom0 or other DomUs unless you write an interface that sits in that DomU and talks directly to the hypervisor (and thus, Dom0) Wine won't help you at all with this... why do you want to access the registry this way?... maybe you can do something else...
