Not a true catholic in the true sense of the word. For a true catholic is a universalist--one who believes that the Lord's Church is universal and has some sense of charity expressed toward brothers in Christ.
Saint Augustine called himself a Catholic back in the 4th Century. He wrote that the greatest expression of "love they neighbor" was to bring an accurate account of the gospel and the true faith to those living in error. I agree with him completely. Jesus asked for "one flock", "one vine", "one faith". The universality of the true Christian Church isn't the embracing of the 25,000 different Protestant denominations that exist today, it's every Christian believing the same thing, being of "one body--one spirit--one hope--one Lord--one faith--one baptism" (Eph. 4:4-5). Luther certainly didn't do anything to foster unity that I can see. His actions brought about the invention of over 25,000 different Protestant denominations, each teaching something different than the others, each claiming to be right.