Not all of Aokiji's attack try to freeze the opponent. See for example Partisan. Don't see why he shouldn't be able to imbue those with CoC if Zoro was able to imbue CoA in his flying slashes.
The point is that Adv CoC doesn't suit their DFs
It's clear that Oda created them without considering them having Adv CoC
Blackbeard too doesn't have Adv CoC
Akainu for example relies on his DF Lethality so much, actually that's what makes him different than other Admirals
Because if we check other Stats, the other Admirals are way better in everything.
So if you say Admirals have Adv CoC then Akainu's Burning Effect becomes useless & he becomes no different than a Boxer
It's clear that Admirals don't have CoC at all