I can tell you that, as long as voltage and amperage requirements are met, you can split those multi-use connectors and use them separately. That's their purpose. The wire colors are fairly standard as to their use.
I noticed my power supplies 8 pin power connector does not match the pin configuration on the mobo perfectly. I did some research and found that all power wires and ground wires match yet I am not sure this is ok. It also appears my eps 8 pin connector can be split in half and be an old 4 pin. My mobo says it will support the old pin configuration as well.
I have seen several posts on the these, yet not one states its safe to use an eps pin in a atx.. grrrr...!!