I'll give my opinion as a [Linux][1] and [HP][2] 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 else.

You'll have a diminished experience with HP hardware if you don't use an OS that HP intends for the platform. That's fine, if you understand that risk. But in cases like this, I recommend that people use something more barebones like Supermicro.

Considering your question is about a basic function like [_booting_ an OS](https://serverfault.com/questions/844750/new-archlinux-install-wont-boot-from-hd-on-new-hp-proliant-gen8), I suspect that you won't find much Arch+HP-specific support here.

  [1]: https://serverfault.com/search?tab=votes&q=user%3A13325%20%5Blinux%5D
  [2]: https://serverfault.com/search?tab=votes&q=user%3A13325%20%5Bhp%5D