jakebohall - 1:22 pm on May 22, 2013 (gmt 0)
The link juice would be passed to the URL that is being linked, and it could create some duplicate content issues. I would make sure to use the rel=canonical tag on the landing page, and take a possible look at query parameters in GWT.
Odds are, the tracking variable is going to make it look like they are a commissioned site. As martinibuster said, if you are just doing this for tracking volume of traffic from the referrer, you should just create a report in analytics to monitor referrers.