B737 NG Captain reported encountering wake turbulence on short final approach to DEN in trail of a B757.

Narrative

DEN ILS35L IFR; contaminated runway; braking action reported good. We were number two and (if I recall correctly) assigned 170 kts. to DYMON. At 500 ft. the preceding aircraft was still on the runway. I advised the FO (First Officer) to be ready for a GA (go around); as ATC queried them to expedite exiting. Approaching threshold they were cleared; at 50 ft.; we got his wake and the aircraft veered to the right. I added power; maneuvered back to the center line. As I was thinking of initiating a go-around we were out of it. Under the circumstances; I made a split decision to continue the landing and land. We touched down extremely soft; to the point that it was difficult to recognize; which might have caused me to hold off the nose a bit longer than usual. At this time the RCAS system activated- LONG LANDING LONG LANDING. It was the first time I had heard it and startled us both. I braked; exited runway; taxied to the gate uneventfully. Afterwards we discovered that the preceding aircraft was a B757.