Doubleseven,  The Idrac is going to be generationally dependent. So if the server is a 12th generation you have to use and iDrac 7 as well as the iDrac 6 with 11th generation servers.  That is likely because the logic for them is based in the ESM/Drac, specific to the card. So if you put the Drac 6 in a 12th generation then it is unlikely to be able to communicate at 100% with the server.  Let me know if this helps.
Is it possible to upgrade idrac6 to idrac7? I am afraid they are different hardware so it's not just a firmware/licence issue. Am I right?
idrac6 -> idrac7 upgrade?