Yes, an Arkansas college prof can legally profit from requiring students to purchase a book he/she wrote for class. (In theory, the book selection should be the best possible for the course.)
Attorney general's opinion says, in summary:
Do provisions of A.C.A. 6-60-601 allow a professor to retain any of the royalties generatedwhen a professor requires students to purchase materials authored by the professor for classes taught by that same faculty member?
RESPONSE: The Arkansas Code contains no direct proscription against a professor's receiving royalties generated by his students' purchase of class materials, so long as the university's policies with respect to the disposition of royalties gives priority to the students' academic welfare. As reflected in the emergency clause to Act 106 of 2007, the only direct mandate is that course materials be selected “without regard to any personal financial gain.”