I'm not a Nexus 7k guy, but I did a quick search and found an engineering document that said that L3 ports on the 7k trust DSCP by default. So as long as your DSCP->CoS and CoS->DSCP maps are set so that COS5 goes to DSCP46, you should be good to go.
If in doubt, though, grab a sniffer and verify the L3 ToS header.