Is it safe to rent a street level unit in the South End? Looking at one on Chandler and nearby.

That neighborhood is pretty safe. Even so, I'd never live on the ground floor without bars on the windows. If they're not already there, maybe the owner will install them?

You can find the crime rate here at crimeteller.com
Thy provide crime map and you can have a sense of crime rate in the South End.
http://www.crimeteller.com/crimetel/crime/us-ma-suffolk-boston.html

not yet