Yes, Core iQ does support the use of emojis within email subject lines. While we don't recommend going overboard, most research has found that minimal use of emojis does not affect deliverability of emails. You can easily add most emojis directly to the Subject Line area in the email template Settings screen. Be aware that if the emoji is not supported by the email client that you are sending to (older Outlook clients, IE browsers, etc), then it will usually default to a ◽ or❓.
We recommend using either Emojipedia for finding the emojis, as their interface makes it easy to search for and copy these items.