http://mangafox.me/manga/one_piece/v56/c544/8.html
In this page BB makes an interesting point: "Your haki is stronger than before, too". Meaning that at this point BB was well capable of feeling even luffy's dormant haki and felt it before in their previous encounter. which also took place before BB's fight with ace. It is completely impossible that ace and BB were unfamiliar with haki before. We specifically saw ace taking a beating from WB back in the day and that was after he fought jinbe. It's virtually impossible that ace and BB were unfamiliar with haki by the time they fougth, we simply didn't see them use hardening.
In this page BB makes an interesting point: "Your haki is stronger than before, too". Meaning that at this point BB was well capable of feeling even luffy's dormant haki and felt it before in their previous encounter. which also took place before BB's fight with ace. It is completely impossible that ace and BB were unfamiliar with haki before. We specifically saw ace taking a beating from WB back in the day and that was after he fought jinbe. It's virtually impossible that ace and BB were unfamiliar with haki by the time they fougth, we simply didn't see them use hardening.