JHU has a sterling reputation for being a top public health school in the U.S.. So, I think the school will always get high caliber applicants. Nonetheless, on this board in the past there have been people who were put-off by the neighbors surrounding JHU, and a small percentage have probably gone elsewhere due to this fact. JHU has in recent years taken an interest in helping to revitalizing areas of the city near the school, perhaps half-social consciousness, and perhaps half to make the area around the school more appealing to students/employees.
The riots aren't a selling point for the school, obviously, but media hype aside they weren't nearly as bad as others riots have been. Personally, I'd apply to JHU without considering the neighborhood issue (or perception of a neighborhood issue), and then if I got in and decided to go, I'd ask other students how to navigate the city safely and where to reside.
From a public health perspective, there are a lot of pressing public health issues in Baltimore itself, such as a very high concentration of HIV+ people, as well as poverty, and probably a myriad of other issues. A pertinent question would address JHU role in the surrounding city, is JHU the isolated ivory tower, or are there related projects in Baltimore for JHU public health students?