When creating a network design that routes an IGP over L2VPNs, with which device does the remote CE router form an IGP adjacency?

Hub site PE routers in an L2VPN do not participate in CE IGP routing; they perform transparent Layer 2 forwarding and are invisible to the IGP running between CE devices.

L2VPN technologies such as VPLS or Ethernet over MPLS extend a Layer 2 broadcast domain across the service provider network, making PE routers invisible to Layer 3 protocols running on CE devices. The remote CE perceives the hub site CE as a directly reachable Layer 2 neighbor and forms IGP adjacency with it. PE routers only perform transparent Layer 2 forwarding between CE sites and do not participate in any CE IGP exchange.

The directly connected PE router does not form an IGP relationship with the CE in an L2VPN design because the PE operates at Layer 2 and does not act as a Layer 3 routing peer.

IGP adjacency is indeed established in this design; it forms between CE routers across the transparent L2VPN fabric, not between a CE and any PE router.