It's not derogatory, it's true, however, most wolf rps out there, yes, I have looked once or twice ;), are less realistic than I'd like them to be. But not for this character.
Personally, I'm an avid fan of realism within fantastical settings, and I do understand your misgivings. If I cannot convince you with this post that I'm not just trying to play a wolf/dog/exotic monster, then I will happily leave it lie and play something else if you'll have the more ordinary character I create then.
Honestly, and this is probably a bad place to start, I am bringing this character forward from other roleplays I have written with him, because I do want to play him again and there are not a lot of giant, three-eyed dog rps out there. But the Anan(as I call them) were not created to be played with others of their kind, they were made to interact with humans or human-like characters. I am not bringing him forward just because I want to play him, but because, to me, it seemed like a good fit. Admittedly, I could be wrong, I'm not infallible, but I read the IC introduction of a character staring at the dead king while fighting goes on in other places and felt that well, honestly, that'd be a great introduction to a pig considering the king landed on the pigpen, but it could also encompass, as I'm sure you were aware, any number of character species, thoughts, emotions and reactions.
Now, to me, a canine's relationship with anything or one is going to be at the heart of the character no matter what. Every character should be shaped by their surroundings, but a dog is going to reflect those surroundings far more readily on the outside than most humans, if violence has been done, then violence or fear will be the reaction. As the Anan are large animals, there'd be less fear involved. As an Anan and not 'just a dog'(there's some really incredible dogs out there *cough*) he'd have the ability to look, see and guage for himself where best to put his anger to use. And if other characters want to temper his actions and put him to even better use, they could well use him as a meatshield, or hold him back for surprise purposes. That would be up to them.
The reason I believe he'd be motivated to react poorly against the invaders is because, if he has been a part of the king's pack for awhile, as he'd see it, then they've just killed the king. He'd have felt it was his obligation to protect the king and he'd be sorely upset that he did not manage it. But he'd also, as a member of the king's pack, see the others who were close to the king as people to listen to and stand beside. Because they still exist, the territory still exists, and if their territory still exists then they should chase the invaders off it. And because he did not manage to protect the king, he'd be extra motivated to protect everyone else, once he's aware of them anyway, his first reaction would be to attack the first enemy soldiers he finds. Yes, it's not quite the we do this for vengeance, I hate your guts, Bernard of Ghant rally that might motivate a character to do impossible things. But he would, rather, be doing it out of a sense of loyalty to those characters the king has shown he, maybe loved is too strong a word, but wanted around him, and out of loyalty to a place the king gave to him to protect.
What I think this character would offer to this particular rp is in the first instance, a creature that could be used by the others to accomplish their ends if they need something of the sort. He is only a smart dog, if they see him as expendable, then he's expendable. If they see him as a glorified messanger, he can be a messenger. If they seem him as a valuable member of this revenge business, then he might well be that too. He'd also be more a protector of them than of their interests, which might help them stay alive long enough to accomplish what both he and they want accomplished. His goal would be to make the soldiers leave and likely to kill their leader because that is what they did to his leader, and while reciprocation won't win the king back, it might cement the idea that they need to leave.
If this is of any use in helping you understand where I'm coming from, great, if not, I shall try something else. No sweat. Thanks for being patient with me.
EDIT: Also, thanks for that further explanation of the magic as pertains to the dog thing. I get it now. I was simplifying things a little in my head. Cool. I like this magic.