The Seattle pro personnel department works in mysterious ways, I'll just say that. Davis is a 27-year old veteran that was an undrafted free agent out of Pittsburgh in 2009, and has bounced around from Carolina (injured reserve his rookie year, practice squad second year before playing in seven games to end the year) to Denver (7 games in 2012) and now here. He's 6'2, 303 pounds.
David Gilreath is a 5'10, 170 pound receiver that has been with eight NFL teams in his three-year career -- the Colts (2011), Rams (2011), Bills (2011), Steelers (2012), Buccaneers (2012), back to the Steelers (2013), Raiders (2014), and now your Seattle Seahawks (2014-present). He was a punt and kick return specialist at Wisconsin from 2007-2010, so that may be the impetus to bring him aboard.
Gilreath was a thing in Pittsburgh shortly -- he caught four passes for 78 yards in a preseason game in 2012 and landed on the active roster for a short while that year.
Anyway -- he hasn't stuck anywhere, but he's obviously got speed (clocked at 4.42 coming out), and agility, and could be an insurance policy in the kick return/punt return game.
Here are his college highlights:
Also, I have to say this is pretty impressive: