I'll give my opinion as a Linux and HP specialist...
There are reasons HP have support matrices and limit what operating systems run on their hardware:
- Support: Hardware manufacturer support is important in a business environment. Even if you don't think it's necessary, coworkers, successors and the company MAY care.
- Predictability: Known platforms to test against.
- Value-added software: Monitoring, alerts, drivers, firmware updates. You lose a lot of these when you don't use a supported OS, so many of the benefits of HP equipment will go unused.
When you operate outside of those constraints, the available pool of people to assist you is far smaller than with a mainstream OS, the types of problems you'll encounter are worse than what you'll encounter with a supported OS, and yes, you'll get responses that will suggest you use something like RHEL or CentOS.
You'll have a diminished experience with HP hardware if you don't use an OS intended for use with the platform. That's fine if you understand that risk. But in cases like this, where you want to use a non-enterprise Linux OS, I recommend that you use hardware that's not as strict (e.g. Supermicro).
Considering your question is about a basic function; booting the OS, I suspect that you won't find much Arch+HP-specific support here.