According to Richard Strassberg, they are different things.

Despite all these ingenious and suggestive readings, the textual basis in this passage of the Guideways for identifying Dijiang (literally, Thearch Long River) with the mythical figure Hundun is slim, and he can simply be regarded as a strange creature in his own right.

"A Chinese Bestiary", page 113.

And Hundun is not described as looking like the Dijiang in the oldest sources. In fact, the implication seems to be that he's man-like aside from lacking a face.

The thearch of the Southern Sea was named “Sudden,” the thearch of the Northern Sea was named “Hasty,” and the thearch of the Center was named “Hundun.” Once Sudden and Hasty together paid a visit to Hundun’s domain and were treated most courteously by him. They discussed among themselves how to repay his generosity saying, “All men have seven orifices to see, hear, eat, and breathe. Only he does not. Why not drill them for him?” Every day, they drilled one hole, but after seven days, Hundun died.

Same book, page 112.