It could raise levels slightly. By Archimedes principle the floating sea ice displaces an equivalent mass of ocean water, so there's no net mass change. But due to differing densities of fresh and salt water, it displaces slightly less volume of salt water than it will contribute in melted freshwater (by about 2.6%, according to [1]). But this may also be complicated by temperature changes [2].

[1] http://onlinelibrary.wiley.com/doi/10.1111/j.1365-246X.2007....

[2] http://onlinelibrary.wiley.com/doi/10.1029/2007GL030784/full