PICO-8 devs use symbols all the time for this jam, and at their heart, emojis are basically the same thing. So I don't see why not! If you can find a way to import them using code only, without using them as sprites, then go right ahead!
why can't i use them as sprites? I use pygame and to make a game with pygame, and i need a window! Can i use circles that are made without importing any image?
The jam's constraints are basically: no imports. So no music imports, no sprite imports. If you use a tool within the code to create a sprite that isn't imported, that's fair game! Make sense?