Hi Andrew,
You can indeed use Emoji in text in CommCare, and as long as your target
platform (say, Android Phones) support the character display set, it will
show.
The reason you're experiencing the issue with Emoji is that the emoji
characters you are using aren't surrounded by quotation marks, like you've
surrounded the word 'smiley'. The characters are just plaintext (same as
english) and thus need to be surrounded with quotation marks for CommCare
to understand that they are a string literal.
-Clayton