There wasn't any need to have Macet be the character on DS9. As shown on TNG, he is clearly not the villain that Dukat was. Macet is a decent, honorable sort. He's every way the opposite of Dukat, really. Somehow I doubt they got along very well as kids.
I'm not sure that what we saw of Macet was necessarily representative of his "usual" self. If we took similar installments of Dukat's appearances in DS9, he'd look to be just as reasonable and honorable as Macet in some episodes, and like a raving lunatic in other episodes. For all we know, Macet was behind the secret shipping in sector 21505, and was deliberately sent to be the liaison because he knew what would be found if things went awry.
The key point is though, there's nothing about Macet that screams, "This guy should have been Dukat!"
I dunno, I liked the Macet character in the novels with the creeped out factor he inspired in people and whispers that he was really Dukat.
I would have paid to see a scene between Macet and Dukat. Can't you just picture it? Dukat: "I simply don't understand why people insist on saying we look alike. You may be my cousin, but I'm much handsomer than you!"
There was never any reason to expect that to happen. Macet was a one-shot character, never mentioned again. (And yes I know he's in the novels). Apart from Lwaxana talking to the computer, there's never been a case of unrelated characters played by the same actor in the same scene. In case such as Data/Lore/Soong or Doctor/Zimmerman, the resemblance was intentional. Jeffrey Combs has said in interviews he imagined doing a scene where Weyoun and Brunt pass each other in the hallway, glance at each other for a moment, then keep walking. Fun as that would be, there's no reason that would happen, other than for the sake of doing it.