Join Date: May 2004
Location: SIN (LEJ once a year)
Programs: SQ, LH, BA, IHG Diamond AMB, HH Gold, SLH Indulged, Accor Gold, Hyatt Discoverist
Posts: 8,816
In F and J, free WiFi is benefit of the cabin class you are traveling in. You just need to use last name and seat number to register via the WiFi portal on board IIRC.
In Eco the free WiFi is a benefit of someone being a Krisflyer member, not by virtue of the cabin class.
So you won't have any issues if in J (Biz) and crediting to another airlines FFP.