As for support, the broad understanding is this:
Fine reading says "Host Access" ...that means storage is accessible.. now if your client is on 4.1 & have thin provisioning enabled, I would assume that they are on VMFS 3.33 ( Not a thumb rule though)
Now reading this, VMware vSphere 5.1
Fine reading says "After you upgrade your VMFS2 datastore to VMFS3, the datastore becomes available on the ESXi 5.x host. You can now use the ESXi 5.x host to complete the process of upgrading to VMFS5."
So what I would understand is that starting from 3.21, 3.31, 3.33 & 3.46 (3.x) should be accessible on ESXi 5.x ( however the usability differs on VMFS versions). I hope that helps. Would love to hear from you about your findings.