The offline co-op is not hidden in a dark corner, it is simply not there.
http://www.nintendoworldreport.com/news/35112
Tom Clancy's Splinter Cell: Blacklist on the Wii U will not have offline co-op.
Producer Liu Jun, of Ubisoft Shanghai, said in an interview with Nintendo Life that "In order to ship at the same time as the other consoles, we unfortunately weren’t able to delve into this feature." He does think that "Nintendo gamers will be really excited to get the game at the same time as other consoles."
Co-Op missions will still be playable online. Tom Clancy's Splinter Cell Blacklist releases on August 20 in North America, 23 in Europe.