Keep in mind that the 6248 is a Fabric Interconnect. While it has functions of a switch, its administration and operation is very different from a standard Nexus switch.
You can use the cable just fine. A passive cable is a cable that has transceivers on each side sending the data with nothing in between but the copper wires. An active able has additional components on each side of the length that are designed to measure, clean, and shape the signal traversing the cable. This is done on longer runs (after about 5-7m depending on speeds, it becomes impractical to do a passive cable).
It's worth noting, that most switches nowadays have the signal shaping circuitry built into the port itself. Those few switches that don't must use active cables for any length. Both the Nexus 5020 and the 6248 Fabric Interconnect have active circuitry built into the port, so you don't need to use active cables unless your lengths are longer than about 7m for 10gb.