iPad does support mouses but normal mouse movements may get accelerated so the positioning could be inaccurate. But you can use "Absolute Positioning Mouse" to know the exact position of the mouse. In absolute mode, HID device sends absolute coordinates to the host instead of x/y delta, then the host sets the mouse pointer to the position without acceleration. So your HID device always knows exactly where the mouse pointer is.

To use absolute positioning mouse, you need to define a new HID report descriptor, from here you can find an example. This project creats a USB HID devices instead of Bluetooth ones but the report descriptor should be same (or similar?).

BTW seems iPhone doesn't support absolute positioning mouse, even it shares most parts of OS with iPad.