This functionality is described in the Internet draft draft-marques-ppvpn-ibgp-version.txt,RFC 2547bis Networks Using Internal BGP as PE-CE Protocol.
To allow a Layer 3 VPN to transport IBGP traffic...
And from experience, PE-CE iBGP works even without "independent-domain" knob
Whether You actually want to use iBGP for back-to-back VRF is debatable since, for starters, RT communities are not stripped by default in PE->CE direction so You have to take care of such stripping manually (if You want/need to, of course).
All-in-all, it's advisable/better to test everything in the lab, of course.