Enlightenment 17 does not support composite so I am not sure why the original poster says he enabled composite. E17 does not need composite for its graphical environment.

For using GNOME applications in E17: this is definitely possible. You can use GNOME applications in any window manager or desktop. They will just look a little different from other applications.

For help in installing custom themes, see this FAQ:
http://art.gnome.org/faq.php

Ubuntu is also not a good choice for using E17 because it lags behind and is not a distribution that the E17 developers focus on. Try Debian instead as one of the developers uses Debian and maintains an official up-to-date Debian repository. This developer also maintains the Ubuntu one but because he uses Debian, the Ubuntu repository is not his main focus. It is also more likely that something will go wrong on Ubuntu as the developer will not be testing the packages on it.