Same with the peach, but now I have to ask, who uses an Emoji in a professional setting? You're skirting the edge of being professional already if you ever use more than ":-)" in an informal Slack message (Aside from close coworkers/friends obv).
Adding a cake emoji to "Happy Birthday" in Slack is nicer than plain text. Younger-staffed start-ups will use emoji alongside "oops", frustration, and/or celebratory statements.