Hi,
If the 5500s are layer-2 with vPC running between them than you can use ISSU to upgade.
here is doc to follow:
ISSU Support for vPC Topologies
An ISSU is completely supported when two switches are paired in a vPC configuration. In a vPC configuration, one switch functions as a primary switch and the other functions as a secondary switch .They both run the complete switching control plane, but coordinate forwarding decisions to have optimal forwarding to devices at the other end of the vPC. Additionally, the two devices appear as a single device that supports EtherChannel (static and 802.3ad) and provide simultaneously data forwarding services to that device.
While upgrading devices in a vPC topology,you should start with the switch that is the primary switch. The vPC secondary device should be upgraded after the ISSU process completes successfully on the primary device. The two vPC devices continue their control plane communication during the entire ISSU process (except when the ISSU process resets the CPU of the switch being upgraded).
This example shows how to determine the vPC operational role of the switch:
link:
http://www.cisco.com/en/US/docs/switches/datacenter/nexus5000/sw/upgrade/513_N1_1/n5k_upgrade_downgrade_513.html
HTH
