Hello @mmercaldieze ,
>> Is there any way to configure an interface in a point to multipoint setup to be part of multiple areas, including area 0?
No, this is not possible in a single OSPF process a single L3 interface can be placed only in one area, the router can be member of multiple areas but using different logical interfaces.
An interface could be in different areas for different OSPF processes but you couldn't secondary addresses to build OSPF adjacencies (this is not possible in Cisco implementation).
>> Unfortunately the VPLS provider will not support a vlan solution
If the VPLS provider is providing port based VPLS you should be free to use your own 802.1Q tags and this would allow to use Vlan based subinterfaces and would solve your issue. You can test this easily.
If the VPLS provider is giving to you a single VLAN VPLS for 50 sites and 5 datacenters meaning that you need to present frames 802.1Q with a specific Vlan -id it is a different question. If this is the case I would discuss with them if and how they can move the service to port based VPLS.
Hope to help
Giuseppe
