ENIGMA's exported C++ is extremely ugly; you won't want to work with it. However, you can work directly with OpenGL by #include'ing it from ENIGMA's Definitions. Open ENIGMA settings, click the Definitions button at the bottom, and enter #include <GL/gl.h> in the code. Unless you save as EGM, your team will need to do the same to use your code.
From there, you can use any OpenGL function ENIGMA can read, which, last I checked, includes all of them.
We normally don't recommend doing that, as it isn't portable; that is, you're stuck with OpenGL on all systems that way. Have you considered creating wrapper functions for the calls you need? Wrapper functions can be ported to other APIs, and odds are, if you find them useful, so will others. That being the case, assuming your needs are reasonably general, we might consider adopting them as part of the official API (meaning, include them in the DirectX port, along with others), if you'd like to share.