Although Connor Vernon and Sean Renfree have not yet been drafted by an NFL team, both have made compelling cases that they could help a franchise. Both have gotten great feedback to date.
The odd thing about the NFL is that the draft at times is inverted: people don't always want a first-round pick, preferring to trade down for more picks. You can gold in later rounds or, on occasion, even in undrafted players.
In the NBA, once you get past the first round, your odds grow much, much longer. In the NFL, it just doesn't work that way.