Dell Power Connect 8024F also support Dell SFP+ cable only...:(
but some cable works properly.
Your problem is same my situation.
Another case is same my Brocade 8000 FCoE switch.
It's also support Brocade product only.
Did you already try to upgrade your Switch firmware to 6.x and check if "service unsupported-transceiver" works for you on SFP and QSFP?
See below from Dell: http://en.community.dell.com/support-forums/network-switches/f/866/t/19581139.aspx