Have you asked the people who put you in that position? They may have a specific role for you even if they didn't verbalize it.

In the absence of other info I would let the more senior guys size him up in terms of technical skills, and instead focus on the more human aspects. At the end of the day what you want to know is "can I be happy working with this person?".

You didn't mention whether this person will be or is likely to become your future manager. If he will then the question becomes "would I like to report to this guy?".