http://www.wisdems.org/news/blog/view/2012-02-faqs-on-the-recall-petition-verification-process
Can Republicans thwart the recalls by running a write-in campaign for Walker during the Democratic Primary?
Any attempts to do this would be unsuccessful under Wisconsin's election laws, because a candidate may not appear on the ballot for as a candidate for both parties for the same office. The recall statute provides that an officeholder is automatically a candidate in the recall election unless the official resigns within 10 days after the original filing of the petition. Therefore, Walker is automatically the Republican candidate for Governor in the recall election because he did not resign within 10 days after the original filing of the petition. Even if a campaign to write-in Walker as the Democratic nominee was successful, the law says that if a candidate is already the nominee of one party for an office, and is also nominated by write-in votes at the primary election to the same office as the candidate of a different party, the candidate does not have a choice, but shall be placed on the ballot for the election under the office and party for which the individual was already a candidate.