In a brief statement, Nvidia said that its membership in the Linux Foundation will enable it to collaborate better with "the organizations and individuals instrumental in shaping the future of Linux, enabling a great experience for users and developers of Linux."
There is quite a bit of room for speculation in this statement, but I would go as far as saying that Nvidia may not have made this move with open-source Linux drivers for its graphics chips in mind. While the company offers a proprietary driver, several hardware vendors and several distributions bundle the open source Nouveau driver, which is developed via reverse engineering efforts. It would be too early to get excited about Nvidia joining the open source effort just yet.
However, the additional Linux activity is in line with previous announcements that the upcoming Kepler GPU is expected to have a strong impact in high-performance computing, including supercomputing. The supercomputing community expects from Nvidia greater flexibility to use their graphics chips, which includes access drivers and also more general ecosystem support within the Linux community.