I had the same issue as you when updating to vMA 5.1.0 1062361 just now.
I also used the real Tools package as opposed to the OSP the vMA is being shipped with and the installation crapped itself there.
I uninstalled the Tools and installed some earlier version of the OSPs (8.3.12) manually, but it still didn't work. Only manually installing the vmware-open-vm-tools-common-8.3.17-870839.sles11sp2 and vmware-open-vm-tools-kmod-8.3.17-870839.sles11sp2 RPMs, which the update was trying to install, solved this for me.
But something still went wrong and made the update fail:
/opt/vmware/var/log/vami/updatecli.log
14/05/2013 10:49:02 [INFO] Running /opt/vmware/var/lib/vami/update/data/job/12/test_command
Preparing packages for installation...
file /sbin/conf.d/SuSEconfig.glib2 from install of glib2-2.22.5-0.6.1.x86_64 conflicts with file from package glib2-tools-2.28.0-3.6.1.x86_64
Uninstalling the package glib2-tools-2.28.0-3.6.1.x86_64 and an dependency finally made the whole update work out.