So you'd like each group as a group to be able to agree on marks and feedback for the single pieces of work submitted by a number of other groups?
I don't think that is possible, but you could get half way there by taking the route Paula suggested but asking them to also complete a Workshop activity for which you create new Moodle groups comprising students from the different original groups, if that makes sense. Each student would then submit the work they originally submitted as a group. Each would make an individual assessment of another piece of group work.
To make the assessments visible to all, you could change the View permissions for students, and also make time for the original groups to come back together and discuss the various feedback they received on the piece of work they have in common, and any insights they gained from their wide exposure to other groups' submissions.
It's a bit convoluted and may not meet your needs - it depends whether the feedback itself is more important than the group process you may have in mind for groups negotiating what feedback to give. If the latter is more important then to the best of my knowledge, it probably needs to happen outside Workshop.