Cant you keep the disks attached and simply install ESXi to a thumb drive without any local storage ?
Of course that will only work if you use some form of shared storage.
It would have the major advantage that you dont need to mess with the existing Raid.
I've been working with HPE hardware since years, and from my experience, I can say that you should not have any issues with this approach (assuming that you are using a SmartArray controller, e.g. a P4xx). Once you add the original disks back into the server, the SmartArray controller should pick up the configuration from the disks.
As mentioned this is based on my personal experience, so please don't blame me if something will not work as expected.