Joe Wilson is a Kerry advisor. He began advising the Kerry Campaign in May of 2003.
There was a thread on FR earlier today about it. The Kerry campaign even pays for a website for Wilson.
Don't have time to find it for you, but it should be very easy to run a search for it.
You should really look it up. The timelines may surprise you.
I am not saying Kerry didn't hire him as an advisor, but it's misleading to say that Bush was merely attacking some Kerry adviser. This was someone the Bush administration used for a specific task, and made a huge incident of it.