I never tried it with Dataform but I use Dataform for group peer reviews every semester. Beside the dataform module, you need to install dataform access entry as block (see attachment). I also added a preset. You need to add groups with a CSV file (see a sample in the attachment) and configure the access entry as a filter that blocks reviews until the user has received a grade. You probably need to set up a second access entry filter for the submission phase so that users cannot change their submission after the grading. The access entry filter worked only once on my site. There seems to be an entry stored in my Moodle database which I couldn't figure out how to delete or overwrite.
With kind regards,