I am not an expert but here is my opinion. Nettles are great, lots of nutrients in them. Bramble you would have to chop it up if it was very woody so it would break down easily. I wouldn't put bramble on however if it had a root on it. I would only put bindwood on if you were very sure it wasn't rooted also, as it is a devil and will grow profusely anywhere. I have it growing up all the way round my lottie fence and it is terrible to shift.
Some might disagree and say that everything rots down if your compost is hot enough but I am not so sure about that especially this time of year. :) busy_lizzie