Although I personally haven’t done it, you can easily P2V Windows servers running on HP Proliant hardware. However, you have major cleanup work to de-install all of the HP-specific software, drivers, agents, etc. If you don’t do this your VM will likely run extremely slow and suffer lots of problems.
To save lots of pain and trouble, you can simply download the HP PSP cleaner. It appears you install it after you do the P2V conversion and it will remove all traces of the HP Proliant support pack. No readme or documentation with it, so you will have to try it out for yourself to see how well it works.
No idea if it supports Server 2003, 2008, 2008 R2, x86, x64, etc. So if you try it out, leave a comment on how well it did or didn’t work and what OS platform.