If it will let you continue and assign the drive anyway, it may be ok.  Firmware on the drive is newer than the others. What version of OMSA are you using? I would suggest you install the latest version. 
I replaced a suspected failing drive in a Poweredge R515 Perc S300. The RAID shows Degraded and the new drive shows Ready Non Virtual. The option to assign Global Hot Spare is grayed out. How can I get the new drive set as a hot spare or is there some other way to rebuild the array. There are 3 good drives in the degraded array. 
Replaced SAS Drive RAID 5 Degraded