I wonder if Media Matters gets any government funding. I wouldn’t doubt it. Leftist orgs invariably do after all, I heard that even racist La Raza and Open Society Institute (Soros) gets grants.
Since Media Matters is a 501(c)(3), donations are tax deductible... So indirectly (getting government support and funding), yes, donations by George Soros to Media Matters are tax deductible.