Ok nvm, i just installed a Windows XP SP3 Professional guest with the Tools-Light from 5,5 Update 1 (without the VMware SVGA II Driver) and the behavior stays the same, display working prior to rebooting the VM after installing the ATI driver, and Code 10 "Cannot start the hardware" after a VM reboot.
Again the only way to get the card working (for a single VM boot of course) is by restarting the Host.
Furthermore i also updated ESXi 5.5 to Update 1 (now running Build 1623387) but the update really only seems to be security related.
This pretty much negates my previous assumption of the VMware SVGA-Driver being the culprit and boils it down to a problem with the specific Hypervisor and/or Version.