Is it necessary to use BUFG for driving icap_clk ?
Is it possible to substitute BUFR (or other buffers) for BUFG to reduce BUFG used numbers.
As long as there are no device limitations that restrict you from clocking the ICAP from a BUFR, then it is OK to replace the BUFG with a BUFR as long as timing is met.
Xilinx does not test the core in this configuration.
It is the customers responsibility to ensure that the ICAP can be clocked via a BUFR and ensure all other restrictions are met.