Can I submit an app to the App Store that needs a hardware device not available in the market(yet)? I am working on a project where im developing a circuit (Raspberry Pi) and an iOS app where the app is used to communicate (via Bluetooth Low Energy) to the Raspberry, only to setup some credentials. The circuit is a prototype, my question is, if I send the app to review will they reject it because the reviewer does not have the Raspberry device to test it?
Yes, you can submit such apps! I have done so before and got them approved.

You’ll probably be asked to provide more information about your setup, or be asked to provide a video of you actually using an iOS device to control the hardware.