Defender Kempf climbed highest from Jonathan Schmid's 30th-minute corner to head downwards and under visiting keeper Thomas Kraft, and it was also a set piece which led to Hertha's quickfire leveller.
Ronny whipped an unstoppable 25-yard free kick over the wall with his left foot, with Freiburg goalkeeper Roman Burki motionless on his side of the net as the ball nestled into the top left corner.
Kraft saved from Klaus and Maximilian Philipp as the home side looked to regain their advantage after the interval, and their second goal appeared to be the winner when it came with 10 minutes remaining.
It was very well constructed, with Karim Guede smartly cushioning a cross from the right into the path of Kraus, whose powerful volley beat Kraft at the near post for his first goal of the season.
There were to be two more twists in stoppage time, though, with Freiburg perhaps thinking that they were home and dry when Nico Schulz was sent off for Berlin following a professional foul.
The red card did not wither Hertha's late search for an equaliser and they found it when another Ronny free kick inside flew past an again helpless Burki and inside the post.
The result leaves both sides on two points from four games and still looking for a first win of the new campaign.