I can't imagine why someone connected to the Brewers would know who Darvish was going to sign with (other than the Brewers, perhaps).
But it isn't unusual for the Cubs Front Office to keep pretty strong radio silence on large deals. I never heard any rumors about the Fowler signing before it was announced, nor had I heard anything about getting Russell from Oakland. Most accurate Cubs rumors seem to come from the prospective free agent or from the potential trading partner, rather than from a Cub source.