Interviewing someone that is a professional interviewer is a challenge. Duh, they know how to give the right answers (most of the time). References are typically as good as they give, why would you hand over a bad reference?
What are some of the things that you look at when looking to hire a top performing recruiter?
Do you mean for corporate or agency? Agree with what Brian wrote, would also ask for either corporate or agency, what percentage of their placements are referrals, and of those referrals how many are from people they've placed. Most people won't know exact numbers, but how they answer will be enlightening. I'd also ask what they feel a good recruiting day is for them, roughly how many interviews, and how many people in general they'll have conversations with during a day, people they are trying to recruit.
On agency side, I'd ask what they billed for past five years.
If you feel, "Duh" about Recruiters who "know how to give the right answers". And their references are also going to be good because "...why would you hand over a bad reference?" Well then--go with recognized accomplishments, e.g., awards, distinctions, accolades, etc. These reflect what others have officially recognized as outstanding performance worth public notification.
However, if you're finding recruiter candidates with no such distinctions/awards/accolades maybe you'll have to get corroborating references on the references that are willing to give a thumbs-up on your prospective candidate(s). An accomplished reference point has significant more value than one coming from a questionable source.