The welding demonstrator/technician on my City and Guilds welding course, possibly the same person Gordon Stephenson has mentioned has a pace maker. I asked him about it a few weeks ago as he was getting it replaced. He said it was safe to weld, he just had to be be careful around HF TIG. This seems a reasonable and balanced answer backed up by first hand experience.
I reckon most GPs that you ask will be guessing as much as we are really.
The welding community doesn't know much about hearts and pacemakers and most doctors will know little about welding and the practical effects on the body and associated electronics. It would be very easy just to cover their backs and say don't risk it but it's probably not a very accurate response.
I am reminded about the joke about a patient who breaks his arm and asks his doctor if he will be able to play the violin once the plaster cast comes off. The doctor says yes and the patient replies " That's funny, I couldn't play the violin before I broke it." Doctors don't know it all.
Just realised this is a bit of a thread resurrection but nevermind the info still stands.