We do not yet know. Gigabyte specifically says ECC memory is compatible, but runs without ECC on their boards. Asrock only says that ECC ram is compatible.
MSI and Gigabyte explicitly mention "(operate in non-ECC mode)".
Is that also true for Asrock AM4 motherboards? Or do they fully support ECC?
From: ASRock Support <snip>
Date: Mon, Feb 27, 2017 at 10:17 AM
Hello,
ASRock AM4 motherboards fully support ECC function.