The idea behind using ndppd is, that you do not need to proxy any single IPv6 anymore.

Lets say the /64 Subnet you got is this:

  2001:DB8:ABCD:12::/64

That's the Subnet of your Bridge:

  2001:db8:abcd:12:1::/80

That's the bridge:

  auto vmbr0
  iface vmbr0 inet6 static
  address 2001:db8:abcd:12:1::1
  netmask 80
  bridge-ports none
  bridge-stp off
  bridge-fd 0

That's your VM:

  iface eth0 inet6 static
  address 2001:db8:abcd:12:1::5/80
  gateway 2001:db8:abcd:12:1::1

That's what ndppd would look like:

  route-ttl 30000
  proxy eth0 {
   router no
   timeout 500
   ttl 30000
   rule 2001:DB8:ABCD:12::/64 {
    static
   }
  }