Ducasse was the Jets' second-round pick (#61 overall) out of UMass in 2010. He has widely been viewed as a disappointment for the Jets. Here's Arif's scouting report on him.
He has the prototypical size (34.5″) and weight (323 pounds) of a top-tier offensive lineman. When at UMass, he was extemely quick and light on his feet, which is why he was initially projected to play tackle when the Jets drafted him in the second round. From what it sounds like, the Jets haven't decided to pursue him in free agency, though it may be telling that some of the best developmental staff in the NFL did pursue him.
The biggest issue coming out for Ducasse was his limited exposure to football. An immigrant from Haiti, he didn't really start playing football until later in his life (though at this point has had about ten years of exposure). His issues in college were all related to experience: technique and play recognition. He did a poor job recognizing stunts and though he had light feet, they weren't often in put the right spot.
Arif thinks that Ducasse will be used as a back-up at right tackle while being expected to kick inside if necessary.
There's no real reason to have an issue with this signing. If Jeff Davidson can mold Ducasse in a way that the Jets haven't been able to thus far, he could prove to be a solid, versatile back-up, and is still young enough where he could be a long-term solution if the team views him as such. If nothing else, he brings in more competition for backup spots along the offensive line, where guys like Joe Berger, Jeff Baca, and Charlie Johnson will be jockeying for position for Minnesota.