Does DNA helicase or topoisomerase actually "unwind" DNA?
Got a short piece of three stranded rope handy? (I don't think they make two stranded rope.) Hold the rope firmly in each hand about 5 cm apart. Twist in the direction opposite the winding. The strands of the rope will separate in the region between your hands. The unwinding and the separation of the strands are, um, inseparable from one another. You can't separate the strands without unwinding.

The heilcase unwinding is merely straightening out the double helix in a very local area. This separates the strands such that one strand can serve as a template for transcription or replication. 

But a consequence of the unwinding in the local region where the strands are being separated, is that other nearby regions get more tightly wound. This occurs because the DNA is far too long for the ends to spin around to accomodate this unwinding. These more tightly wound areas are what is refered to as supercoiling. The topoisomerase alleviates this stressful coiling. https://en.wikipedia.org/wiki/Topoisomerase

So, the answer is both helicase and topoisomerase result in the unwinding of DNA.