OK if GPS1 Vcc different from Pixhawk Vcc?

Hi, I have a Pixhawk Orange Cube that is powered by a LiPo battery. I am also using a companion computer to communicate with the Pixhawk over GPS1 via UART.

Is it important that the Vcc / GND of the UART serial connection have the same potentials as the main power bus of the Pixhawk? Or are they unrelated?

Edit: Just to clarify, the setup in question would have both Vcc’s at 5V, but not from the same 5V source, and the grounds would not be common.