He'll first need to make the team on special teams. In college he was an excellent ST player. He's a smart, hardworking player and if healthy he will be a surprise contributer.
HUH?
He will line up at a position, not create one no one has seen before.
Every defense accounts for 11 players, whether Mills is at TE, or FB, or Hback, he would be accounted for just like whoever else would be lined up there.
Hback was originally 'created' by Joe Gibbs back in the Hogs days.
Basically you take either a FB or a TE, in a 1back offense, and line him up on the wing. (Imagine the position where the 3rd TE lines up in goaline situations)
Most times you put him in motion to either lead block as a FB would, or get into a pass pattern as a TE would.
I guess you could either describe it as a FB plays closer to the line and goes in motion to lead the play, or a TE who plays a step back off the line.
Basically its a cross between a FB and a TE in skills needed as well as utilization.