Using servos with pixhawk

[Quest]

Pixhawk instructions warn not to use servos on the transmitter when pixhawk is connected to RX with SUBUS. I have a FRSKY X8R set up to use 16 channels 8 on SUBUS and 8 on the RX, is it safe to run servos, relays and and switches this way or do I need to provide additional power to the RX? There are a few you tube videos showing this being done but I don't want to fry my Pixhawk.