Blair was not a traitor, but he did defect to the Borderworlds making him and the rest of his comrades an enemy to the confederation. Blair simply could not choose a flag over his friends.
However its really a question of loyalty and confeds values. Blair did SEEM to regret defecting for a short while since it meant betrayal, but realised that it was not him that broke his 'oath of loyalty' to confed but that confed simply broke theirs to the citizens of the terran confederation.
We may think that perhaps Tolwyn did see Blair as a traitor to humanity rather than just to the confederation, ultimatley, in his mind. But then again...he simply discarded Blairs image as the great Heart of the Tiger, and made him seem as the enemy and a traitor to confed simply because he wanted to win the backing of Paladin and the rest of the assembly in confed to see through an intergalactic war that would of kept the confederation 'at his feet' and prepare for the REAL enemy to arrive.
I would think that Eisen and Blair went renegade and their public image painted with the words of traitors to confed.
Now...how exactley can you defect to pirates???