Not at all! If you feel you can make a fangame in a 3D space with 360 degree movement or a platformer with 2d movement, you're more than welcome to!
It can be tricky to figure out what constitutes a Yume Nikki fangame, but the main thing is being inspired by certain formulas- collecting items, exploration, surrealism. But don't let the restraints of RPG Maker stop you!