Unfortunately...Yes, its nor supported. Since this is not supported, Its not recommended in the production environment.
Hi,
it is defenitely not on the HCL.
http://www.vmware.com/resources/compatibility/search.php
Maybe there is a member out there who has installed 5.5 on a DL380 G5.
But if it is your production env. don´t update
Frank
You can install it, but not something I would use for production, you are leaving yourself a bit exposed running on hardware on the HCL list. Consider upgrading your hardware or upgrade to the 5.1 in the meantime.
Even if its not on the HCL, it should still work.
it essentially means that HP didn't pay to make sure that the hardware is certified for this release since its end of life
However it won't be supported by vmware in case you need assistance.
So if it's production, I wouldn't update.