An awakened animal can't be a companion, neither can a Magebred animal.
Actually it is stated in 5 nations that you cant take the two magebred animals in that book as animal companions.
Where did you find that in Five Nations?
Right in the section on the magebred bear and tiger. They state that you can take either of them as level 7 alternate companions.
As I recall, there was some specification about being from the region... but that's hardly an impediment.
I've always been a bit confused about animal companion adancement... I've been told they get feats (and it would suck balls if they didn't) but what about ability scores? I saw somewhere that they don't advance in skills... maybe it's the same deal...?