As far as my experience goes, you have to have a Nat type 1 on PS3 for Crysis 3 to consider you to have an Open Nat. Other games eg CoD say Open for Nat type 2.
I don't think having a moderate nat is much of a problem anyway, having strict would be more concerning.
Side note: On my home internet playing C2 (and C3), I was ALWAYS moderate nat no matter what settings i used on my modem (DMZ, UPnP, port forwarding). When I hooked up a 360 with C2 with the exact same settings, it read Open Nat. Make of that what you will.