The dists from Pikefarm are untagged and are bundled with gmp and nettle (snapshot_export).
OK, but you can easily avoid using them in the build, can't you? Because Debian generally prefers shipping "official" tarballs (so that you can easily compare checksums).
I'm not sure that autogenerating debian/changelog entries is that meaningful. They should at least say "UNRELEASED" instead of "unstable", to reflect which versions have actually been in Debian. Actually, all the versions uploaded to Debian have been odd-numbered snapshots, contrary to the plea in packaging/README.
The "orig" tarballs made by Marek also contain autogenerated documentation (modref and traditional_manual), which the official tarball does not. While not a technical problem, it's still not quite right, I believe.