I have a customer who is looking for a split Micro-USB cable, which has one USB-A host connector on one end and two Micro-USB cables on the opposite end (they will be plugging into cameras). Can I simply wire it like this diagram I've attached? I believe he has software he is experimenting with where he is trying to control two cameras simultaneously. I've seen "zipper-stlye" split Micro cables like this. Is this simply the operative wiring? Thanks in advnace, friends.
This does not work. You will need a USB hub.
The USB Y cables you have seen use two USB Type A male plugs to one USB B type plug. Only the power lines are split to the extra plug.
This is not conform the USB specification. But it is a small hack to have more than the standard 2.5 Watts of power available, it is used for 2.5" hard disks that can't spin-up with just one plugs worth of power.
If you look at these cables you mentioned - This one, claiming to be the "original", is one example, and their site does include a circuit diagram that makes it clear, you will see that either the type A connector is typically slightly larger than a normal one, or there is a small box in the middle of the cable. This is because USB hub electronics are hidden inside, rather than it being a simple plug connected directly to the wires. There's likely no particular advantage (other than space saving) over using a standard hub.