Is the interface fully routed? FreeBSD handbook has instructions on Bridging. I know apple devices using bridging in their network stacks also. (it is not necessarily secure that is a separate matter). See the handbook try making that interface a bridge interface see if it works. Are you sure you don't need bluetooth? I keep on hearing apple say make sure bluetooth is enabled for the iphone to pair with the imac but unsure if that is required to use iphone as network card. I know win10 is always trying to hack into my iphone despite that i've disable every option I can find to prevent it from doing so.
(I had issues connecting a linux machine to imac. I enabled bridging on the linux machine and it automatically worked well without any further adue)
I would NOT call what your trying to do a "time saver". Already you have down time. If bridging doesn't work I would say: plan to spend more time. FreeBSD is not intented to make apple pairing easy and you should mark your time sheet accordingly. It may be true FreeBSD needs to rethink if things should "just work" not favoring the server-world idealogy nothing works without configuration and hacking. But that isn't up for discussion here. And really, there are powers who don't want freebsd to "just work", there are software wars where version hacks are made pretty much just to stop freebsd (or who else) from contending.