Cat, I see what you're thinking, and it's not necessarily a bad idea*, but the core word of this thread is animation.
The goal is the animate everything in-camera, to help stretch the skills and abilities of the participants. It's also designed so that anyone can enter, even if it's only with a handful of bricks.
Some of the challenges require a bit more in terms of bricks/resources, but as the rules say:
but also possible to make in stop-motion by a typical brickfilmer
Typical brickfilmers can do the animation, but few have the digital programs and/or knowledge to work with CGI.
It's an idea, and Nathan would certainly be the final authority, but for now I'd say no.
This is about using in-camera and animation techniques to achieve the desired look, and CGI enhancements/additions, while not explicitly outlawed, are at least partially against the basic premise of the thread.
*In fact, the main reason a lot of VFX look poor in brickfilms is because they don't understand the proper relationship, and there's nothing in-camera to support the digital additions. So it's very important, and a needed skill, but perhaps not something for this thread.