Upgrading from vCenter 5.1 to 5.5 via fresh install and license migration.

Hello,

I am wanting to do a staggered or slow upgrade of our VMware Infrastructure to 5.5 from 5.1.  My plan is to spin up a new server and install from scratch VCenter Server 5.5 on it.  Then enter in the license key we have on our 5.1 VCenter Server into it.  After this is done, I would disconnect the 5.1 ESXI hosts from the old vcenter server and re-attach to them on the new 5.5 server.  Assuming this is possible, what happens to the ESXI licenses, will they remain attached to the hosts, or do they need to be re-entered on the new vcenter server?  If everything up to this point seems reasonable and error free, IE Vcenter Server 5.5 can manage 5.1 hosts.  Then I would start slowly moving through all of the ESXI hosts upgrading them to 5.5.

Do you see any issues with this plan?  I dont have any complex setup, like HA or DRS.  Just a bunch of simple local disk based hosts being managed by vcenter.  But I don't want any "license rent seeking spookyness" happening, like the hosts somehow reverting to 60 eval mode.  I am guessing the licenses that I have (Standard and Enterprise Plus) for Vcenter 5.1 and ESXI 5.1 will work with 5.5 without issues, it's only once you try to move to 6.0 that you need new keys?

Thanks for all of the information you can offer.