I've tried this recipe and found it bloody good. I thought the blended onion/chilli gave it a good body (not an original idea but good nonetheless).
I've blended them raw, with a tablespoon of water, using a hand blender in a narrow container, and turned out great. Sometimes have to add another splash of water depending on how it looks. It should be quite thick.
I don't think a Kenwood 'jug-type' blender will work as it just throws the ingredients around the jug. A hand blender lets you push the mixture down whilst blending and gives great results.
Hope that helps