The equipment rule trumps the "other source" rule. As for Warforged, I imagine that is dependent on how you and the DM handle his transformation. If the PC becomes a robotic, Warforged version of the beast a la Transformers, then it should work but he will not be able to pass for the creatures on close inspection without something like an illusion. If it is magically becoming that form and so being biological, you certainly couldn't benefit from it as you have lost the source.