Use iPhone camera as an input sensor for EV3 As EV3 has Bluetooth builtin as well as iPhone too, is there a way to connect them somehow so that iPhone could send data from the camera via Bluetooth to an EV3 brick?

As a more general question, can I make iPhone send/receive data to/from the brick via Bluetooth, e.g. commands, with Objective C or other ways?
I haven't come across any existing projects like this yet, but there is nothing stopping you from doing this yourself. I would suggest writing an app for your phone in Obj-C and just remote controlling the EV3 via bluetooth.

The bluetooth communication uses the RFCOMM profile. This post might give you some hints on getting the bluetooth connection.

You can find the EV3 communication protocol specifications in the hardware developers kit that is linked in this blog post.

Hopefully this is is enough to get you started.