So far yeah I think the only admiral that might be loyal to a fault is Akainu because of the whole Dog thing but if written well fierce loyalty can still be great character
Greenbull~ I wouldn't say I'd 100% loyal to wg but he's an Akainu Simp so long as Akainu is loyal, he'll be loyal
If Akainu turns against the upper echelon of the WG, I'm not sure Greenbull would follow. After all, Greenbull has been portrayed more to be exactly like the Celestial Dragons with his over-the-top, "you have no human rights!" type lines.
Akainu is not like that, in principle he wants to protect the common people from pirates, or maybe more accurately his sole goal is to eradicate piracy. He's been blinded in that pursuit, and now he's waking up to the reality that there's an equally if not bigger evil going on right under his nose. All this while he's been stuck to his desk, clearly having wanted to get out into the fields himself, which he's definitely going to do now.
That's my take at the moment at least, maybe I'm totally wrong.