Yes, you can code straight in OpenGL with C++, you just have to have, and include properly, all of the headers for it. People have literally been coding games in OpenGL and C++ without an in between for decades. Now, considering you had to ask this, I feel I'd better warn you. OpenGL is not a Game library, its a Graphics Library, and it will *only* handle 3d and 2d graphics. It will not make it easier to handle input, audio, networking or anything else. OpenAL is an Audio library. If you're looking for something in C++ that makes the entire process easier, I'd instead recommend SFML or SDL2. SFML and SDL both use OpenGL for graphics, and SFML even supports direct calls to the OpenGL library, while still using its other available functionality.
Edit: Also, you need to keep the discussion going in the threads you've already created (you've got at least 2 threads about OpenGL and using it for 3DS homebrew development that are within a few days of each other, and now that I've seen that, I'm assuming that this was part of that same line of questioning), and when you make a new topic, do not just put things like C++ or OpenGL, put things like "How do I code for the 3DS using OpenGL?" so people more immediately know what you're looking for. This will make it easier for people to see whether they can actually answer you or not. I am not editing my original answer, because it answers the question you asked and gives some advice. But SFML and SDL2, as far as I know, do not work with 3DS, you'd be better off finding a library specifically targeting the 3DS. The way you ask questions, open threads, and the questions you ask all tell me you are rather new to this, and I'd suggest you do a lot more reading about OpenGL, C++ and how homebrew gets ported to/made for the 3DS first.