I don't know if Ace was on Im black list like BB and Luffy are but given the fact he is a D. and the son of the former pirate king it is very likely that Im didn't have much love for him. Aka kill him no matter what just like the marines were doing, same thing they tried to do with Luffy at the end before Shanks stopped the whole thing. So I guess that, in the impossible scenario a CD popped out if the blue in front of Akainu just like Shanks did, if a CD with that mindset (let's say Mjosgard) appeared with that order I guess that or the marines already step on him, via Sengoku or whatever, or, worst case for the WG, his order pass but the guy is executed short after.
Afterall if a moron simply jumped in and saved Ace life, pirate king seed, that would be a big blow to the whole organization, Im too given at that time he was probably the D. with most potential (if we exclude MC privileges of course).