AS I understand it, you have some inquiries related to the connection of VCCR_GXB when the XCVRs are not used. For your information, all the VCCR_GXB must be powered on even though the XCVRs are not used so that the device can operate properly. You may refer to the C10GX pin connection guidelines -> "Table 9. Transceiver Pins" -> "VCCR_GXB[L1] [C,D]" section for further details.
Please let me know if there is any concern. Thank you.