For the same reasons that Human points out I would tend to say no, very unlikely IMO.
However, I would argue that it was likely that, due to the specific purpose of the party, that those who knew of the party would have held high expectations that the Wetterlings would be attending. There would have been an opportunity for someone to plan an abduction based on those expectations. I'm not saying that I think that's what happened, but it does leave that door open in my mind. Popular notion is that the decision to attend the party was last minute. I do not believe that to be true.
What is the 'specific purpose of the party'? And regarding WS, it's been the assumption that the Wetterlings attending the 'party' was last minute. If you believe that not to be true, then what?