Wake had 7 sacks in 7 games before tearing his Achilles tendon against New England. Oddly, all seven sacks came in the last 3 games, including one in the game he was injured. He had four sacks against Tennessee.
PFF's metrics should be taken with a grain of salt, but they consistently rank Wake as one of the very best pass rushers in the NFL over the past few years.
Prior to the injury, Wake was almost an ageless athlete, similar to John Abraham a couple years ago. However, Achilles injuries are notoriously tough on players who rely on explosiveness. Maybe Wake can overcome it but between that injury and his age (34 next season) he's a high risk player.
I think he makes perfect sense for Seattle as a healthy Wake is one of the best pure pass rushers in the NFL, and if he busts Seattle has the depth at pass rusher to get by without him. The injury and age concerns will likely keep his pricetag relatively low. Plus he'll be a released player and wouldn't cost a comp pick.