Yes, it looks like the IceCore is using the same AC-coupling and no-level-shifting approach @mattvenn uses in your link... apparently it works, but it is definitely outside of the DVI / HDMI specification, which specifies 0.4V peak-to-peak:
(pulled the above table from Lattice's own RD1097 - LatticeECP3 HDMI/DVI Interface document for the ECP3)
The DVI specification gives the same numbers...
So I guess, if it works it works? But could be detrimental to your TV / monitor in the long-run to be operating outside of spec?