The biggest difference is that a single, long exposure, photo is a single read off the sensor and the video stacking isn't, it's a sequence of frames, probably taken 25 or 30 times in a second.
In terms of single versus stack, well, I can think of a few things to bear in mind with video:
- Video frames are usually smaller in size (length/width) so level of detail for same field of view will be sadly lacking.
- You may need hundreds, or more, video frames to get the same exposure time.
- You may need to boost the ISO to get a reasonable amount of data in the short sequence of time between reads on the sensor.
All in all, I'd suggest you'll get much better results with a single shot. Stacking, by the way, is common in astrophotography, though, as @jrista notes in the comments, you can't get the long exposure effects of light blur with the source removed as a result of speed of movement.