See Figure 6-2 Converged Multi-hop FCoE Network Design Using FCoE NPV
http://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus5000/sw/operations/fcoe/513_n1_1/ops_fcoe/ops_fcoe_npv.html
You have to use NPV on N5k, there is no FC interop support on N5k, to connect to Brocade.