Well the icons are mostly in /usr/share/icons, so they won't be touched, you would just have to find out how to alter the default icons in E17 and change them for the Mint versions. As for themes I just don't know, you would probably have more luck asking that question on an E17 forum. Alternatively just try it out for yourself, E17 will be added as an alternative login to Gnome, it won't replace it, so you can't lose anything, and if it doesn't work for you just uninstall it, adding a different window manager is one of the easiest and safest modifications you can carry out on a Linux box.
Fujitsu Lifebook AH532. Intel i5 processor, 6Gb ram, Intel HD3000 graphics, Intel Audio/wifi. Realtek RTL8111/8168B Ethernet.Lubuntu 13.10,Ubuntu12.10 (Unity), Mint16 (Cinnamon), Manjaro (Xfce).