I forgot about Windows 7 in all honesty. Apparently the Mac emoji keyboard can be opened with ⌘+CTRL+Space.
You can get Roblox Studio to run on Linux-based devices (including Chrome OS) using Grapejuice. Although it was a terrible experience on my Chromebook and not worth doing.
A basic set of emojis will show if you have the “Segoe UI Emoji” font installed (they’re usually black and white glyphs, however), but Roblox actually includes an emoji font (TwemojiMozilla.ttf), so it doesn’t matter it your system supports emoji or not; it also keeps emojis consistent between devices.