They've got a hefty patent portfolio, but I can't think of a recent example of them using it to freeze everyone else out à la eInk. Of course, the barrier to entry into their market is so incredibly high that there would be only a small number of companies who'd actually be able to test that. The only instance of them really going after someone (over IP) that I can think of was in the 80s when Hitachi was pretty brazen in the way they were stealing source code. Very low effort, like: Step 1 - acquire from a subcontractor the entire source tree for IBM's current mainframe OS; Step 2 - sed s/IBM/Hitachi/g; Step 3 - package the OS with Hitachi mainframes sold in Japan. They got along famously though, after Hitachi lost the legal battle and started paying them a royalty for the rebadged OS.
IBM does have a reputation for buying competitors in very niche areas, like process planning software, and then not doing anything with them except maybe parting them out several years later. It looks suspicious, but I think that is more to do with the way they stick to hyper-specialized enterprise solutions... the pickings are naturally very slim.