My question is whether you can't use discretion in deciding to probation someone who doesn't seem to have the reputation of someone who is likely to be a repeat offender. I'm not questioning whether you are within the strict interpretation of the rules to put him on probation, I'm questioning whether you are fomenting good will while teaching the lesson. According to Snapster, woot has in the past been very lenient with Adder, considering the sort of behavior he has exhibited. Yet, I don't recall SkekTek having ever broken a significant rule, other than perhaps some petty baiting of the mods sort of things- seems to be a much better sort of individual to exhibit some discretion about to me.
Generally speaking, the leniency comes into play regarding the severity of the punishment, not the application of it. In some cases, not outright banning them is the leniency.
However, it looks like someone could mistakenly include the StreetTeam referral in their link and not know it was a referral program, since it applies to all Threadless users. With that in mind, I'm going to remove the probation, but now that the warning is out there, I hope not to see the links any more.
Note that it looks like it requires extra effort on the part of the user to include the links, since a great many users link to designs without including the referral code...