Does students asking questions in class improve the learning outcome of the entire class?
In a group class setting, educators, mistakenly, think that if one person responds, subsequently the rest of the class shares the same understanding. Most instructors would agree this is not the case.

Questions on relevant topics help to engage all the students. Often times I use the student's question as a connecting point to ask one of mine. Other times I involve other students by asking questions such as “Good, now can someone provide another example? Who else has an opinion? Who disagrees?”

If the question is off-topic then it is the educator's responsibility to bring the class back to the discussion by asking one of their own questions.

At this time, I am unaware of any research related to this.

Note: I will append any links to this post if I come across relevant studies.