The short answer is: No.
You will need two licenses, one for Jira and one for Confluence (or any other Atlassian application outside Jira Software).
The reason for this is simple: Your Jira and your Confluence are two separate installations with, potentially, two completely separate user bases.
If you are using EasySSO with Jira Service Desk and an attached knowledgebase in Confluence then your user numbers for EasySSO need to match the user base, not the number of agents you have in Jira Service Desk. This is because EasySSO uses IOPLEX Jespa to authenticate your users. (See here why) IOPLEX Jespa does not recognise the difference between an agent and a customer the way Atlassian does.