I think in a very real sense, you are, in fact, interviewing potential advisers. It would be rather disingenuous for a potential adviser to believe that he or she is beyond the bounds of accountability for his/her research record. I would say something such as the following:
I am interested in participating in publishing papers. Would we be able to publish papers together?
What types of projects/papers have you worked on in the last few years?
What are some of the current papers or projects you are working on?
A quality adviser would have quality answers for these questions. Moreover, they would know that it would play in their favor to have at least some explanation as to why they have not published lately. These questions will open the door for them to provide an explanation of their research record. If they seem to dodge around that time period, I'm honestly not sure that they should be your number one choice for an adviser.
I would also verify that this is not just a matter of their CV being out of date. Perhaps they have published papers and just have not updated their CV in a while.
Aside: If I can give my personal thoughts on choosing a young, unproven adviser, I would recommend avoiding professors who have not established themselves somewhat. I have seen a number of PhD students who run into issues when they choose a professor who has not yet been given tenure and who is constrained by the "publish or perish" mentality.