If Namor is unfriendly to Zoom, can Zoom use Hypersonic Speed to move to square A?

A - Target square
N - Namor
W - Wall
Z - Zoom

A N
W Z

Characters can not move through squares occupied by opposing characters or blocking terrain. Walls act as blocking terrain.

It sounds like Zoom will not be able to move to square A because he would pass between two squares that he can not pass through, but I can't find anything in the rulebook saying either way.

That's because no such rule exists. A wall and a figure on a diagonal don't create continuous blocking terrain for any moving purposes.

Just to be clear, your example should look like this:

A N
W|Z

And not like this:

A |N
W|Z

Right?

If so, then as Hero_guy stated, there is nothing preventing Zoom from moving into A.