Brewster Would have knocked Haye out! Vlad was totally superior to Brewster, proved it in the rematch when Vlad was not drugged.
Helenius dropped Brewster in the 4th round. Helenius also knocked Brewster to ring corner later and Lamon would have gone down if not for the ring post
Haye has a much better amateur pedigree and better overall boxing skills, make no mistake about it. Still, head to head in their primes Brewster would be a very tough matchup for Haye. Brewster showed on two occasions that he can digest extreme amounts of punishment (vs. Wlad I and Krasniqi) and still come out on top, knocking out his opponent. Plus he walked and overwhelmed Golotha in 120 seconds. Easier boxer to handle for Wlad? Probably Brewster rather than Haye. Brewster liked to come forward and engage in the open. Haye doesn't. Wlad doesn't look as good against guys who try to stink it out in the distance while waiting for a hole to counter. Brewster H2H vs. Haye is a different story though.
Brewster was battle-tested. A rugged tough guy who could take a punch and would take a couple to give one. That's an important attribute for any HW to have--the ability to take hard shots from another HW. I do not believe Haye can take HW powershots, but I do believe he is more skilled in other areas. Whether or not Haye can put those skills to display without getting caught remains to be seen.