I am a little confused, so forgive me if my comments are off target.

In the 2014 E38 OEM configuration the Starter Relay Type is set to "Apply to 12V". When the key is turned to the Start or Crank position, 12 volts is sent to the BCM. If the BCM and ECM "agree" that it is OK to engage the starter motor, the ECM will then send 12 volts from J1 pin 52 to the low amperage side of the Starter Relay. The low amperage side of the Starter Relay is grounded in the wiring harness (chassis ground). This closes the Starter Relay, engaging the high amperage side of the relay, and sends 12 volts to the starter motor.

Without a BCM, the ECM will never activate the Starter Relay. Changing the Starter Relay type to "Apply to Ground", changes the ECM output (pin) that is activated (in this example grounded) if the BCM and ECM "agree" that it is OK to engage the starter motor.

The VATS patch will allow the engine to run without a BCM, but the Starter Relay will need to be rewired for direct (or manual) activation.