We aren't talking of wild theories here, the technique has actually been used. So was the blood on the nettles real or simulated? We don't know but the possibility of simulation, far fetched though it might sound, has to be considered.
It would I imagine be incredibly rare to have an example of such simulation at a potential crime scene. But the forensic scientist MUST always be open to such a possibility. If Dr Kelly was murdered then we aren't talking about casual criminality here. The perpetrators are likely to be the security services from this or another country. If it was a case of murder dressed up as suicide then we are talking of the need for a good deal of sophistication.