Yes; however, I've never heard of a Pro Artist nominee being disqualified because his/her work "did not appear in a professional publication." There is a pending constitutional amendment that would add the following underlined words to the section on notification and acceptance of a Hugo Award:

Section 3.9: Notification and Acceptance. Worldcon Committees shall use reasonable efforts to notify the nominees, or in the case of deceased or incapacitated persons, their heirs, assigns, or legal guardians, in each category prior to the release of such information. Each nominee shall be asked at that time to either accept or decline the nomination. If the nominee declines nomination, that nominee shall not appear on the final ballot. In addition, in the Best Professional Artist category, the acceptance must include citations of at least three (3) works first published in the eligible year.

And there is the matter of what actually constitutes "a professional publication." For example, assume for the sake of argument that theresamather receives sufficient nomination votes next year to be asked to accept a Hugo Award nomination, at which time she is asked to cite at least three works first published in 2007. She can then point at her official web site and say, "I use this as a vehicle for selling my artwork professionally; therefore, it is professional publication. I'd not want to be the administrator who rejects that statement and disqualifies her.