Thumbs have value because they take time to create (and they become a derivative work), unless you use shitty automatic creation. Some webmasters may also not like you using their db as they've spent the time to load, check and review submitted galleries.
Some may even pursue legal action. Try copying some of thehun's descriptions and links, see how fast the C&D arrives.
I would ask the webmaster, the worst they can say is no. But I wouldn't just take them without permission.