When I invert my Y axis in the control menu, it also inverts it for my splitscreen friend. Likewise, when he un-inverts his controls it does the same to my controls. It's impossible for two local splitscreen players to have their own independant controls. This is a glaring mistake and I'm unsure how it made i past quality control, hopefully it will be fixed ASAP.
This was actually pointed out in a review.
"Then there’s Guerrilla mode, which is Future Soldier’s take on Horde mode. It’s for up to four players, either online or split-screen (note, there’s no option for players to have specific control set-ups, so if one of you inverts their aiming controls then affects everyone on the team)"
While Mush himself obviously didn't know, there must have been a dev or two who read that comment and investigated. I should imagine they already know. I hope.