Assuming they can.
Yes: Hackett has been an exceptionally productive per play receiver since seeing his first snaps in 2005, posting DVOAs of 15.5%, 35.7% and 10.0% 2005-2007 respectively. His 2007 was particularly exciting, as Hackett had 3 highly productive (and 100 yard+) games in a featured role. He had 4 contests in which he recorded 6 or more receptions, of just 6 games total in which he played a significant number of snaps in. That's an important symbolic breakthrough for a player who had shown an ability to maximize his touches, but trouble getting consistently open. In his previous 28 games he only recorded two games w/ 6 or more receptions. Even though Hackett may be pricey, especially for a team without a ton of cap room like Seattle, he may be among the best values available. If he can put his injuries behind him and build on three seasons of exceptional promise it's not a stretch to say he's on the cusp of being an upper echelon wide receiver. With Deion Branch out and Engram coming off a career high in receptions and thus more than likely a career high in tackles, the Hawks are terribly thin at wide receiver. They have depth, but no playmakers, no deep threat and only Nate Burleson as a viable red zone target.
No: Hackett is a great talent and good fit for this or what looks to be Seattle's next system, but his health has mushroomed from worrisome to potentially deal-breaking. He missed all of his first season with a hip flexor injury he couldn't adequately recover from. He's both injury prone and a slow healer. Further, his injuries are not of the freak variety but consequence of typical NFL play. Severe sprains can increase the possibility of recurrence as we witnessed in the Divisional round where Hackett reaggravated his injury after avoiding a big hit by Atari Bigby. Though Seattle looks desperate for receivers, they do have significant bench depth. If any one of Ben Obomanu, Courtney Taylor or Jordan Kent step up, or if Branch is able to return or Engram able to stay healthy, Seattle could survive with a mid-level draft pick or free agent. The West Coast is demanding of a receiver's skill but not his talent. Since 2000 the list of receivers who have posted 10%+ DVOA seasons in Holmgren's system is both long and modest: Sean Dawkins, Bobby Engram, James Williams, Darrell Jackson, Joe Jurevicius, Hackett and Jerheme Urban.