Yes, this is definitely an issue we have all faced at one point in Workfront. ;)
So the bad news, you won't be able to do groupings on the "Other Teams" really since it is a multiple select field. Besides, it would look weird because you'd have grouping for each possible combination you had.
As for filtering, there are things we can do with EXIST filtering that has worked for me. Can you give me a little more detail about what reporting you are doing?
- Object of the report (task, issue, assignment, etc.)
- How many teams are you filtering on?
I probably have something similar I can give you to tweak and then copy and paste in. ;)