As far as making camera screens and the like, probably not as that would require full access to the rasterizer code to render the scene for each camera location and I don't think that kind of access is going to be possible without Halo's source.

However, I've been trying out an idea to steal a texture when it's created in DirectX and copying what's on the screen to that texture so that something like the sniper scope could be achieved, but it's not working for some reason.