If dont know what breed my mare is and i breed her to a purebred arabian stallion can I register foal halfarab?

I have always delt with purebred arabs so this is new territory for me. I recently got a mare from a friend who bought her at an auction and she has no papers. She looks Arab, but could have morgan in her, they look similar. Can I breed her to a registered Arabian stallion and then register the foal as a half arabian for show purposes? The AHA rules online are somewhat unclear. It states the "grade" horse can not be a purebred unregistered arabian, but what if you have no clue what the horse is? does anyone know? Thanks for the help!