Most likely, he did not approve. David McCullough's biography infers that those who blame Truman for setting the conditions for the Vietnam War are incorrect, that 'he never intended for the CIA to become what it did' during that conflict, and that he held to his intended, more limited approach, during Korea.

You pointed it out first, but make of the the non-commenting what you will; from the McCullough book (which I highly, highly recommend):

Lyndon Johnson came to Independence several times again, hoping to enlist Truman's endorsement of the war in Vietnam. But Truman, who as President had first pledged American support for the French against Ho Chi Minh, made no statement about the war. Privately, he had become more and more disillusioned with Johnson's leadership.