Careful, though, because just being a critic doesn't mean he isn't susceptible to the same sorts of biases and issues that cause a lot of other medical papers to fail. I'm hoping he's on the paper because they ran it by him for a thumbs-up before submitting it.
I hope he is not on the paper for that reason as this is basically honorary authorship. If he just reviewed the paper before submission then he should be in the acknowledgements.