With every passing hour I think of another possible way to interpret your question
When you say "have to go through OpenGL" are you using OpenGL for most of the drawing (ie you want to go *around* OpenGL to update textures but then keep drawing with OpenGL and the updated textures) or are you asking if you can program the 3D hardware directly and do cool texture update things without using OpenGL at all ?
If the former, previous answer stands (you can do it but you need some API extensions in OpenGL to deal with things like establishing addressibility and cache flushing to pick up the new contents from memory).
If the latter, the answer is "yes", but you'd probably want to implement some kind of 3D API yourself anyways.