It's so hard to tell if they do. We'll never know. They design lots of stuff and spec it out to companies. Heck Apple, Samsung, Galaxy, Maytag, Ford, NASA, clothes (everyone and everything), all spec stuff out and have a factory build it.
It's all about the design, having great engineers, the choice of using high quality Mosfets, caps, etc etc when they spec the board for the factory to build, and strong factory floor presence and strong QC back at the ASUS engineering facility. If you build 150,000 Mobos and can save $4 on each one by using cheaper caps in the power section, you make more money, all companies try to maximize profits.
Like cheap PSUs, or quality PSUs. Lots of times you get what you pay for.
For example:
We buy knife block cushions made by a secondary supplier for $21 each. They warp and crack. They have a factory make them. The OEM of our equipment sells them at $52 each. They don't make them, they are made a different factory, and the OEM has better specs for their choice factory. They don't warp or break. These two sellers don't make the part. A factory does. They both are the exact same size and look identical. One is made better.