Hi Subhajit,
problem seems to be solved with an update of the HBA's firmware.
We've previously checked for firmware updates through the ILO / Intelligent Provisioning and there seems to be none available for our HBA's, but following your suggestions we're able to find and download an update from HP' web site (v. 1.98). It has then been applied trough VMware's ssh shell.
After a reboot of the hosts both cloning from a template and vmotion completes without hanging at 40%.
Thanks for your support.
Ass-DGM