As far as I know, Gifs can't be used in Construct 2, you would have to seperate those images and put them together in the Animation Editor Area of an Sprite.
But yes, it is possible, I did it already. The loading Layout is just there to load the Game itself. The Loading Layout itself will only take the important Stuff that is actively being used on the Loading Layout.
But don't put more stuff in the Loading Layout then needed. A Percentage Bar or similar and a Logo/Animation should be enough, otherwise It could take too long just for the Loading Layout to load itself.