You can mix and match as you please. I always keep things as GPT as I can. The partition table compatibility is dependent on the bootloader and OS being able to read them. So since the ones we use around here do both, it doesn't matter. I think this is actually a pretty handy way of getting around the windows requierment of MBR/bios and GPT/UEFI requirement. You can make a windows drive MBR and another drive with GPT and put Linux, BSD, or whatever else you want on there.