I’ve just finished doing this during my show reel development, to check the animation timing against the background and to see how the BG renders in terms of lighting and such. I rendered @ half scale (full size is 720p) so it wouldn’t take forever. The BG is mostly textured planes, so that rendered in full fairly fast, but because of the lighting setup, including the animated character really pushes the render time up. So I did OpenGL of the figure animation after cranking out a full-rendered background plate.
If in the Render context you set the Shading>Alpha: option to Premultipled, and render to RGBA PNG format, you can put the resulting OpenGL animation image sequence in the VSE and slop-comp it over the rendered BG using the Alpha Over Effect strip.
In general I didn’t use the Textured Solid mode because my textures look very odd without the full Material shading, but you can do this if your material/Texture is fairly simple and uses only a single texture. However at one point the character interacts with one of the tetxured planes, and in that instance, I rendered a black “card” with the chracter on Open GL, then the art for the card as a separate plate using Textured Solid, then added that to the VSE compo using an Add effect strip.
Upshot is that the OpenGL can be composited just like any other rendered element, depending on how you set it up. It’s a fast and accurate way to check on many aspects of a final rendered scene before actually spending time rendering. My graphics card isn’t GLSL-capable, so I haven’t tested that aspect. but for the most part, OpenGL is WYSIWYG, so you should be able to use it for some lighting and texturing tricks if your card can manage.