The algorithm can only reuse combinations of patterns that it knows about, it can do extrapolation but it often ends up being just like a blend. However, you can give it multiple images and it'd borrow the best features from either—for example drawing from all of Monet's work. (Needs more optimization for this to work though, takes a lot of time and memory.)
As for the images, as long as the type of scene is roughly the same it'll work fine. The fact it can copy things "semantically" by understanding the content of the image makes it work much more reliably—at the cost of extra annotations from somewhere. With the original Deep Style Network it's very fragile to input conditions, and composition needs to match very well for it to work (or you pick an abstract style). That was part of the motivation for researching this over the past months.