Hello,
When you check interoperability, it's not so much the vCenter version you're worried about, but the ESXi version. For instance, downgrading ESXi hosts to 5.1 while keeping vCenter at 5.5 might work just fine and be supported.
You can go here to check for storage array compatibility
VMware Compatibility Guide: Storage/SAN Search
And check IBM's compatibility matrix, as well. They may only support a subset of vSphere features at the moment with the code versions you're running.
Cheers,
Mike