Of course. The basis for Marxism is a dialectical approach to understand history and philosophy. Marx built on the work of Smith, Ricardo, Kant, Hegel and many others. He also worked very closely with Engels. A marxist today is someone who uses dialectical materialism to analyze contemporary politics and economics. Of course Marx used the tools he developed to understand politics and economics in his time, so he is a Marxist. However, he really disliked the designation of “marxist” and would probably not have called himself so.
A good review of Marxism can be found in a book by Ollman, Dance of the Dialectic: STEPS IN MARX’S METHOD