Hi
All of the adapters required for integration are 10gb, so you need to have 10gb ports availed on the fex.
Also I noticed you mentioned you are using the 2248 FEXes, note that this FEXes are only support until UCSM Firmware version 1.4, so if you are running anything newer than 1.4 you will need to use the 2232 FEX model as the 2248 FEXes won't work.
See configuration guides below
UCSM 2.0 c-series integration
http://www.cisco.com/c/en/us/td/docs/unified_computing/ucs/c-series_integration/ucsm2-0-2/b_UCSM_202_C-Integration/b_UCSM_202_C-Integration_chapter_01.html#concept_774B705BE3594D4EA81050E408629FEE
UCSM 1.4
http://www.cisco.com/c/en/us/td/docs/unified_computing/ucs/c-series_integration/ucsm1-4-2-0-1/b_UCSM1-4_2-0-1_C-Integration/b_UCSM1-4_2-0-1_C-Integration_chapter_0100.html
Let me know if this helps