-Be sure the PCIe lots are enabled on the BIOS.
-Check that the cabling is being done properly, be sure that the SAS cables connect the server´s backplane to the UCSC-MRAID12G V01, short read about cabling:
https://www.cisco.com/c/en/us/td/docs/unified_computing/ucs/c/hw/C220M4/install/C220M4/raid.html#70368-Re-seat the raid controller.
-On the Power-on-self test (POST) you can check if the Raid Controller is being initially recognized.
-A firmware mismatch between the Raid Controller and the other components is a common cause of a Raid Controller not being recognized.
-You can try re-installing the current system firmware with the HUU, that way you could be sure that the Raid Controller Firmware is on a compatible version with the rest of the components.
-If you need the storage with urgency you can try using the Embeded Raid Controller but they only support SATA drives I believe.
If, After that troubleshoot you are still having problems I'd advise to open a case with TAC and to let them know about all the Tshoot you already did.
Hope that helps.