As far as I can find out it’s impossible to connect directly. Apple is very restrictive, to bypass their ‘location services’ needs a jailbreak. We use Bad Elf GPS devices because they are one of very few that are useable (licenced) with Apple.
I’m hoping to set up a Reach as a base and Ntrip caster to enable DGPS on the Bad Elf Surveyor and get sub metre precision into the iPads that way. Ask me in six months if it worked or not. )