The answer to the question posed in the title is "yes, by three percent". The experiment was conducted with a general diversity statement on 14 MOOCs with 29,000 students. The authors suggest that more directed diversity statements might attract more under-represented people, but this is difficult to do with a single welcome page. Interestingly, "we implemented a diversity statement that both focused on equality and the value of diversity. This may have caused large and ultimately attenuating variation in the effects on women, older people, and people from less developed countries, while lower-SES learners interpreted the statement more as a cue about requisite prior knowledge."