The Oakland Raiders have done quite well in the Reggie McKenzie era finding contributors in undrafted free agents. Some of the finds by McKenzie Marquette King, Jalen Richard, Denico Autry, and Denver Kirkland, among others. There have also been some nice finds of players who are no longer on the roster, like Rod Streater.
And the Raiders didn’t find him, but Donald Penn is more of the more notable UDFA’s in the NFL. So despite a player’s draft slot, or lack thereof, undrafted free agents are important parts of NFL teams. The Seahawks and Patriots are model franchises for that.