Can this done direct from esxi 4.1 to 5.1 update 1 using the update-manager?
Yes, you may use direct upgrade path for 4.1 to 5.1, with update manager or cd installer using of the binary "
VMware-VMvisor-Installer-5.1.0.update01-1065491.x86_64.iso"
This is supported path, you may refer to this release notes. http://www.vmware.com/support/vsphere5/doc/vsphere-esxi-51u1-release-notes.html
