I signed up for the forum here to provide some help. I've been tasked at work with setting up an Asus ROG G751j with Windows 8.1 and 7 for dual booting. The way I was able to get it working was:
1.) Disable secure boot in the BIOS (Tap F2 right away after a cold boot).
2.) I installed a 240 GB SSD hard drive to install Windows 7 on
3.) Booted from the Win 7 install disc and installed to the new SSD.
At first it would crash when attempting install but after disabling secure boot it fixed the problem. After the installation of Windows 7, the drivers had to be loaded. To do this, I went into device manager and pointed each device missing a driver to the folder on the original system hard drive named "eSupport." This found the wireless driver and a few others. Then I just auto searched for most other devices. Keep in mind, a laptop is just a bunch of products from other manufacturers, so if you know the make and model of the hardware you want to load drivers for, you can usually find the drivers you need on that manufacturers website. Anyway, for the graphics, Windows wanted to load a generic driver, and since this model has the nVidia Geforce GTX 970x chipset, I went to nVidia's website and found the drivers I needed. Windows 7 definitely works on this hardware.