Gemini 11 had some success with a similar scheme involving tethering themselves to their Aegena craft and spinning up. However this was far from straightforward and only created tiny amounts (Wikipedia says 0.00015g) of artificial acceleration.
In order to get 1g from a 50m tether it would have to spin at a little over 4rpm, which seems like quite a lot for such a big thing. Also the difference in acceleration between an astronaut's head and feet would be something like 0.3 m/s/s, which hasn't (AFAIK) been tested.
The Gemini experiment was amazing (especially given it was some way down the list of mission objectives) but I don't think it qualifies as a full demonstration of the technique. I know this project is not intended to be a finished design, but they give the impression that artificial gravity generation is a solved problem.