Yes I hope it can. You can also use Python code within KNIME and combine it with other functions. If you have a working Python file why not give it a try. Otherwise there are free (Vernalis) and payed (Selenium) tools to harvest data from the web.
Concerning JSON you will have to define a pattern (XPath) for the data in order to transform it into a usable table.
So if you could provide us with an example this might help. And if it comes to predictive models KNIME also has you covered there.