No John, it's easy. The gear blank and hob rotate together, so the hob naturally cuts that correct helix angle automatically. Just line them up perpendicular, the same as they are on the lathe.
If you think about it you're just making a toothed worm, exactly the same as the existing worm in shape and size and position, and it is gradually cutting its way into the blank by rotating together, the same as the original gear train meshes. This results in exactly the proper form teeth for the gear to fit the hob (and worm).
Another analogy is that this is very similar to how a tap works. Yes the threads are at an angle, but you drive the tap vertical to the work, and by rotating it cuts the angle automatically.
In fact a rotating tap can be used, in a suitable fixture with a gear blank, to create a worm gear that fits a threaded rod of the tap's pitch and diameter. Then, a piece of threaded rod, end turned down to a journal, can be used as a worm for that gear.
If an Acme tap and threaded stock is used, the gears are very similar in tooth form to standard worms and wheels.