Teammate interviews for the public are fluff, so that's not giving you anything.
Example: Nobody here had any signs that Sammy Watkins could struggle with sobriety, addiction, and depression in Buffalo (which came out years after he left). All signs were that Watkins was a high character player, person, and a great teammate.
Do you have the film to consistently watch a player run his routes when he's not the primary read? These would be great things, but it's not widely available for the fantasy community to accurately assess.
I think drive and passion would be great things to know, but I question how you'd be able to accurately assess it for each player you're interested in.