About clock gating setup & hold check, different clock gating cell (such as AND, OR and NOR etc.) and different active edge of launch/gated clock will make this checking several combination. you can refer to the timing report and review your design to understand more and more. One article on solvnet is very helpful for you:
<<How Are Clock Gating Checks Inferred>>
Hi...
I do not know much about it.....but as much i know is as follows.....
setup & hold time values required in this check are mainly the function of cells used in clock gating, it is not bad to say it is a functional of library you are using.