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 just need to choose this person from the list in Respondents and Requests section of your report, that's all.
Make sure you added team( if you didn't, click on "plus" sign and follow the instructions on screen):
2. Choose respondents in Respondents and Requests section of your report: