VandenHurk was optioned to Triple-A Norfolk after the trade, and third baseman Josh Bell was recalled from the Tides.
The 32-year-old Ohman was 0-0 with a 3.30 ERA in 51 appearances during his first season with the Orioles.
"I thought there was a possibility. Nothing's ever certain," Ohman said. "You're with the team that wants you the most, so I guess my time here is done."
"Anytime you get traded, it's a good feeling to know that you did well enough in a place that you were to merit the trade. There's somebody else out there that thinks you're serviceable. In that way, I guess, it's a compliment."
To make room for Ohman, the Marlins sent right-hander Alex Sanabia to Triple-A.
VandenHurk, 25, allowed one earned run in 1 1/3 innings and two games for Florida, and he was 8-4 with a 4.68 ERA in 98 innings for Triple-A New Orleans with 87 strikeouts.
Orioles interim manager Juan Samuel said the deal was made shortly before the 4 p.m. EDT deadline for non-waiver trades. Samuel is managing his last series -- the newly hired Buck Showalter takes over next week.
"It came right down to the wire, as we were looking at the time and we thought, 'Well, nothing's happened,' and then the next thing you know, my phone is ringing and we lose Ohman," Samuel said. "He was somebody we relied on to be our situational lefty out of the 'pen."
Earlier this week, the Orioles traded infielder Miguel Tejada to San Diego.
"You wish those guys well. ... The same with Tejada when we lost him the other day -- he got a chance to play for something," Samuel said. "I know a lot of guys who were probably a little uncomfortable this time of the month not knowing if they were staying here or not. We do the best we can with what we've got and it's just unfortunate we lost those guys."