The HipChat <-> JIRA integration currently is limited to associating a specific room with a given issue. If you're looking for a general list of users, that is only available from within the HipChat client itself.
If you're running the desktop app it should be very quick to switch over and open a chat with a given person (you can CMD-TAB to the app and use CMD-N to quickly open a chat with a user.
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.