No they are not. No worse than other GMs, that is for certain. He's hit on his fair share.
Do some reading on his use of the draft, and you'll find he's generally regarded as one of the best:
http://www.packersnews.com/story/sports/nfl/packers/2015/07/21/data-shows-just-good-thompson-draft/30475885/
2005 - Aaron Rodgers - Grade A
2006 - AJ Hawk - Grade C
2007 - Justin Harrel - Grade F
2008 - No 1st, traded. Jordy Nelson first pick. Grade A
2009 - BJ Raji - Grade A, Clay Matthews - Grade A
2010 - Bryan Bulaga - Grade B
2011 - Derreck Sherrod - Grade F (But injuries were the issue)
2012 - Nick Perry - Grade C
2013 - Datone Jones - Grade C
2014 - Ha Ha Clinton-Dix - Grade B
2015 - Kenny Clark - Grade Incomplete, but early returns look good.
He hit on Rodgers, Nelson, Raji, Matthews, Bulaga, Clinton-Dix, and it appears Clark.
Middle of the road on Hawk, Perry, Jones (Hawk is controversial, but held down the position for a long time. You can't suck and have that happen. Perry has played well the last two seasons. Jones I'm leaning toward a lower grade, but not a complete miss.)
Missed on Harrel, Sherrod