Hello vmklaus,
it work smooth, and you have two options:
a) download file from VMware "VMware-ESXi-5.1.0-799733-HP-5.34.23.zip" (found on https://my.vmware.com/group/vmware/details?productId=285&downloadGroup=HP-ESXI-5.1.0-GA-10SEP2012) and place into Datastore.
Then SSH to your ESXi and fire following command:
esxcli software profile update -d /vmfs/volumes/[your datastore]/[your folder]/VMware-ESXi-5.1.0-799733-HP-5.34.23.zip -p HP-ESXi-5.1.0-standard
b) download file from VMware "VMware-ESXi-5.1.0-799733-HP-5.34.23.iso", burn the bootable HP-Branded ESXi 5.1 Installation on an CD for further deployment.
Don't forget to load the Updates, found on http://www.vmware.com/patchmgr/findPatch.portal
Please bear in mind that the actual HP SmartArray Driver has a bug. It shows an alert on the Firmware, even if you load the actual Firmware.
Regards,
Josip.