OpenGL is used to display the data in the viewport within Daz Studio. I can’t speak for how this works internally, but it’s likely the same ‘instance’ of the OpenGL object dealing with the final render which is why obscuring the viewport might mess up the render. Of course, this is largely guesswork, but it would have to be something along those lines, since if it created a new instance it could in theory render the image to a new (hidden) buffer. Either that or the problem is cross-talk between the two instances.
But I’m getting over technical here. The upshot is if you intend to use OpenGL for renders those are the issues you’ll contend with.
Off-topic, and I apologize for over-emphasizing this, Quality setting 4 (ie, 3Delight render) is intended to be ‘final output’ quality, while the others are more suited for test rendering rather than the final image. To get the most out of any work, you will most certainly want to add good lighting, and shader lights like UberEnvironment have zero presence in OpenGl renders. In other words, it’s like they don’t even exist. If you’re getting fast renders with 3DL then chances are you’re not using any lights, and that means it’s only using the one ‘headlamp’ attached to the visible camera (if you don’t have an actual camera, then the Perspective View camera is used).
There are a plethora of tutorials and helpful folks here, myself included, which can point you in the right direction to make superior work in a very short time compared to the results you might get from the OpenGL renders. Some talented folks whom I am not fit to kiss the shoes of have produced breathtaking images using 3DL. I daresay you’d be hard-pressed to find many which were rendered with anything less.
So, yes. Strong emphasis on moving up to 3DL because that’s where the real power is. Come to the dark side, we have cookies!