First, I'll talk about the premise information.
In normal Meraki MX behavior (without BETA function), SD-WAN fabric routes are always advertised by OSPF.
Strictly speaking, Meraki MX does not track Auto VPN Peer state. Therefore, routes will always continue to be advertised in OSPF.
And, Meraki MX cannot learn OSPF routes. In effect, it only uses OSPF to advertise Auto VPN Peer routes.
This behavior reduces the likelihood of Auto VPN Route flapping within the OSPF area.
In my opinion, I think that if there are no circumstances to divide an area, it can be set to area 0.