I tried compiling a ROACH2 design that used a 300 MHz aux_clk as the clock source, but it failed in the mapping stage. It turns out that the aux_clk MMCM parameters are hardcoded in such a way that the effective limit on the aux_clk input frequency is 100-200 MHz.
This is an artificial limitation due to the hardcoded MMCM parameters, so perhaps someday the allowable aux_clk frequency range will be expanded. Hope this saves someone else from scratching their head too much, Dave
