Updating to ESXi 5.5 was a pretty straightforward task overall. One of my ESXi hosts upgraded without any complications. The second host hung during “relocating modules and starting up the kernel” of the initilization of the installer.
Some searching around lead me to this post with two resolutions. First was the boot option “ignoreHeadless=TRUE” setting. For my particular configuration, this was unsuccessful. The second option was to disable the ACPI headless extensions with the BIOS which was successful for my Asus Z8PE-D18 board. Below are some screenshots of the BIOS setting.
Hopefully this helps someone else searching around for ESXi 5.5 installer hangs or freezes at relocating modules and starting up the kernel,