Can VCCR_GXB, VCCT_GXB and VCCH_GXB be connected to GND following the fitter report when only the IOPLL is used, but the transceiver or the fPLL is not used in Intel® Arria® 10 devices?

No.  Due to a problem with Intel® Quartus® Prime Pro Edition Software version 19.2 and earlier, the fitter report may incorrectly say VCCR_GXB, VCCT_GXB, and VCCH_GXB pins should be connected to GND when only the IOPLL is used, but the transceiver or the fPLL is not used in Intel® Arria® 10 devices. 

When the IOPLL is used in Intel® Arria® 10 devices, VCCR_GXB, VCCT_GXB and VCCH_GXB pins on a side where used IOPLLs reside need to be connected to proper power supplies respectively. 
Refer Intel Arria 10 GX, GT, and SX Device Family Pin Connection Guidelines for detail.

This problem has been fixed since Intel® Quartus® Prime Pro Edition software version 19.3.