No. The 80/20 ground beef is not the same as ground chuck because the ground beef and ground chuck have different nutritional values to them.
Ground Chuck has a higher fat percentage than the ground beef does.
As for the 80/20 ground beef it means that the ground beef is 80 percent ground beef meat and the other 20 percent of the ground beef is fat content.
So you get 80 percent actual meat from the 80/20 ground beef and then the other 20 percent is fat content.
The 80/20 ground beef would be healthier though than the ground chuck because the 80/20 ground beef contains less fat content.
However there's also a different taste for some people when it comes to eating ground chuck versus 80/20 ground beef.