As noted on Reddit, the Apple TV is now listed on the VUDU UHD compatible device list, and the VUDU Apple TV app, which was updated today to version 1.1.0, confirms that 4K and HDR support is available.
Disney content is available through iTunes on the Apple TV, but Disney does not permit Apple to sell its offerings in 4K due to pricing issues, giving Apple TV owners few options for watching high-quality Disney content on their set-top boxes.
The VUDU app on Apple TV does not let users to rent or buy movies or TV shows directly on the device, but content added to a VUDU user's collection from elsewhere, such as the web, will show up on the Apple TV and will be available for 4K playback.
Most Disney content in UHD quality on VUDU is priced at $24.99, but other 4K titles can vary in price and are around $15 to $20. VUDU has several purchasing options, such as standard definition, high definition, and for some content, disc + digital.
The VUDU website features support for renting and buying more than 100,000 titles, plus it allows for linking an existing UltraViolet or Movies Anywhere account. All of that content, both linked and purchased on VUDU, is available on the Apple TV.