By default, reviewers can add comments to your Articulate Review content items without creating an Articulate ID. This makes it even easier to gather feedback from your stakeholders. They'll just be prompted to enter their email address to post comments. (If their email address is tied to an Articulate ID and if they aren't already signed in, they'll also be prompted for their password.)
And if you want to require reviewers to sign in with an account, you can do that, too. Just open your content item in Articulate Review, click the Share tab in the upper right corner of the screen, and uncheck the box to Allow comments without signing in.