No, it's not the same as adding a hub. There is a limit to the number of endpoints a single controller can support - that includes devices hooked up through hubs. Maximum USB Device Count on Intel 8...

The Rosewill card was just an example - I don't have any experience with it. There's plenty of cards to choose from so feel free to pick something you're more comfortable with.

But installing a...

That does seem like a fairly small amount of devices to hit the endpoint limit unless all your devices are USB 3.0.

If you're running out of USB endpoints then you have to add a new controller....