We just got a bunch of new Dell servers with current vSphere & vCenter versions (5.5, with possible future upgrade to 5.5U1). We'd like to add our older Dell R300 servers (Xeon 33xx series and onboard SAS6/iR controller, currently running ESXi 5.1 and still under support contract) to the same vCenter but Dell and VMware say they only support up to vSphere 5.1U2.
Now we need to choose between trying to run everything on 5.5 (if it runs on the R300s) or downgrade newer gear to 5.1 (we can still do that since the newer machines are not yet in production) or run a vCenter 5.5 with some 5.5 nodes and some 5.1 nodes until we refresh the older hardware (will probably be in the 12~18 months range).
Is vSphere 5.5 actually incompatibile with R300s (i.e., won't run) or is it just not covered by "official support" because they're older servers but runs anyway?