Of course he had haki, he wouldn't have lasted in the NW without it.
Doubtful. Ace had an extremely powerful Devil Fruit ability, so it's not like gaining Busoshoku Haki was a bonafide necessity for him in terms of being able to carry out a lot of offensive power the way people like Luffy, Doflamingo, or Cracker do. The Whitebeard Pirates also demonstrated very good teamwork during the war, with knowing to avoid Whitebeard's Quakes without communication, being able to swap in and out of battles without missing a beat(Jozu intercepting Aokiji for Whitebeard), and being able to coordinate attacks(Marco and Vista able to attack Akainu together despite being in a moment of severe distress).
There's also Blackbeard's comments about Ace not having been hit in a while, something he'd be aware of since he fought alongside Ace for a number of years, which indicates that Haki wasn't something Ace had to deal with for some time. Buggy also refused to attack Ace because he knew that Whitebeard would come after him, so that's implication that Ace could have simply avoided many a fight due to Whitebeard's name, allowing him to navigate the NW more safely than the average Logia. Ace also demonstrated to have outstanding physical abilities by keeping up with Jinbei for five days, someone wielding something strong to his DF, and Van Ogre's comments that Ace was a fierce fighter despite losing his DF powers.
It's very likely that when Ace encountered a situation that needed Haki, he could have just had another WB member proficient with the skill, like Marco or Jozu, sub in, or overcame it with other abilities, including his powerful DF. Ace being a Logia that survived well in the NW doesn't guarantee he was a Buso user. Hopefully, the novel clears it up once and for all with a precise answer.