In a match-up of past Delray Beach champions, German second seed Haas squandered three break points in the 11th game of the third set.
Gulbis won the last five points to hold for a 6-5 lead, then won six of the last seven points in the tie-breaker.
France’s Roger-Vasselin upset US top seed John Isner 6-4, 4-6, 6-4 in the other semi-final. Roger-Vasselin became the first Frenchman to reach the final of the event but he had to work for it by overcoming 21 aces by Isner in the match lasting more than two hours.
Gulbis, ranked 109th in the world, is seeking his third ATP title at the same event where he won his first tour crown in 2010.
Former World No 2 Haas, ranked 90 spots ahead of Gulbis, was denied a chance at a 14th career title at the same event where he won the 2006 crown. Haas last won a hardcourt title in 2007 at Memphis.
Before this event, Roger-Vasselin had not made it past the quarter-finals at a ATP Tour event.