Matrix_get and matrix_set can be used for matrices used for the current camera view. If you're needs are more complex than stock gamemaker cameras can provide, you can set them yourself provided you have built them with matrix_build functions. Camera_apply will also apply the matrices for the given camera to the current render.
This video covers how to translate 3d world vertices to 2d gui vertices which might help. I'm sure there is a way to calculate view width and height from a matrix transform, but I don't know it off the top of my head.
Don't know if there's the answer you want here, but I hope I might've pointed you in the right direction.