No, you don't need to. Standuply takes a list of users from your Slack workspace. So if the person you want to add is a member of your Slack workspace, you need to choose this person from the list in the Respondents and Requests section of your report, that's all.
Make sure you added team( if you didn't, click on the "plus" sign and follow the instructions on-screen):
2. Choose respondents in the Respondents and Requests section of your report: