Mate is configurable just like Xfce.
You can find most customizing options here:
You will find Appearance there.
Next you select Theme.
After you select Customize, you will find options for Controls, Colors, Window Border, Icons, and Pointer.
As you see, you can choose the preinstalled themes and find options to customize it.
As you see, there are more options to customize your install.
So technically you can mix few themes and icons. You can mix themes and icons.