Yes, if an emoji is added to a NON-MMS or a SMS message, the message will more than likely be processed as multiple messages. 

Why? Emojis are not created equally and some require additional characters to display in a text. 

Depending on the length of the message, and the number and type of emojis used, the text will use more than one message credit to send. In the majority of cases the text will count for 3 message credits. 

The system has been programmed to warn against additional credit use. Please take note of the credit use indicator below the text message box to see how many message credits the text will use.