Jeff Niemann, formerly of the Tampa Bay Rays, will turn 31 in February and has not pitched in the big leagues since the 2012 season. He had shoulder surgery last year, and there has been very little buzz about him on the free agent market this winter, which is understandable given the dicey recovery that follows shoulder surgery.
Before that, Niemann was a decent starting pitcher for the Rays, compiling a 4.08 ERA and 4.23 FIP between 2008 and 2012. His 6.76 strikeouts and 2.93 walks per nine innings weren't spectacular, but they were good enough for him to pitch in the big leagues regularly. For his career, he has a 101 ERA- and 105 FIP-, both of which suggest he's been slightly below league average.
If Niemann is healthy and willing to accept a minor league deal, it couldn't hurt the Mets to bring in a little more starting pitching depth, even with the arms they have in their farm system. A recently injured pitcher might not be the best backup plan for Jenrry Mejia, but the more starting pitchers the team has available, the better.