An important point of clarification when talking about the Southern part of Dallas is that "South Dallas" is the name of an actual neighborhood, located around Fair Park (where the Texas State Fair is located). That area is historically one of the most neglected and impoverished parts of Dallas, and many commercial developers have come in to demolish the old and build new. There is certainly opportunity there, but you have to keep in mind it's more of a long play in terms of when the area will be more of a C or B type neighborhood.
Another area that comes to mind when people say "South Dallas" is Oak Cliff. People who don't live down here couple these together but there is a lot of history and they have distinct names, so it's good to know the differences when investing down here.
Oak Cliff is also an area experiencing a lot of development and growth, but there are many well established neighborhoods in Oak Cliff with a lot of value already such as Kessler Park, Winnetka Heights, Wynnewood North, etc. Getting into the neighborhoods on the outskirts of these areas certainly provides some great opportunities. Many homes in Oak Cliff were built in the early 1900s all the way up through the 70s, and there's a lot of opportunity for homes that need remodeling.
Hit me up if you want to chat more about areas around here. I live in Oak Cliff and do a lot of business in Dallas proper. I've sold homes in South Dallas, Oak Cliff and beyond.