In the recent episode,
Subaru Okiya was confirmed to know Conan's identity when he caught Conan pretending to be Shinichi over the phone.[7] Based on some of the questions he asked Ran, he may have deduced Conan was Shinichi much earlier,[8] but had lacked absolute proof up until the phone incident.
Quoted form http://www.detectiveconanworld.com/wiki/List_of_characters_who_know_Conan%27s_identity
This proves that Subaru is not Akai, and he is still uncertain about Conan identity until he peeps Conan using the voice changing bow tie and confirmed his identity.
While Akai already knows Conan identify long ago during the early black organization incident, although is not been revealed.
He's been investigating Conan & Haibara during the early episode, the battle against Vermouth.
In fact, the FBI wasn't stupid enough not to know Conan identity like Jodie & James.
Also if he(Akai) is confirmed to know Haibara true identify, so is pretty easy for him to figure out Conan identity as well.
Akai is not stupid, make no sense if he was still uncertain about Conan identity.
Another theory is that Akai already knows that Conan has a voice changing machine, so there is no point for him (Subaru) to peep on Conan using Sinichi voice.
In the ending of Rena Mizunashi Hospitalize episode, When Akai questioned Jodie about on handling Rena disappearance, and Jodie replied that Conan will take care of that.
Conan use his bow tie to act as Rena Mizunashi to get a holiday form the production company to avoid suspicion that something has happened to Rena.
Conclusion, Subaru is not Akai!!