I agree w/CarolMN about a conference call not adding any guarantees to the rental scenario...but there are advantages to doing one...decisions on whether to wait list, change resorts or accommodation size, etc can be made "on the spot" if both the renter and the rentee are on the call...and it does provide some comfort, if not a guarantee, to the non-member renter...
As for the identifying information the member has to provide at the beginning of the call: I've been told (never tried it, tho) that MS will let the member call, give the ID info (member number, etc) and then let the member conference in the renter...
So, three-way calls can be a good thing for both parties...even if they don't add much in the way of guarantees to the transaction...
At the same time, MS may provide options to the renter that you as an owner may not be comfortable with. I wouldn't want to do a waitlist from SSR to BCV/VWL which would take more points from my account, particularly with automatic waitlist, with a renter. I'd rather leave the whole waitlist idea out of the option list. A three way call may have my renter agreeing to the waitlist with the MS rep, putting me in the middle and having to say "no." Or MS may say "I don't have a studio but I have a one bedroom - and I might say "I don't have enough points for the one bedroom" - meaning I don't want to rent that many points and have MS say "oh, of course you do, you just borrow some from next year." MS may forget on the call which voice is the member and which is the renter, and agree to do things the renter asks for that leaves you in a spot - and if you aren't a fast thinker, you could hang up the phone without really realizing what you did.
So while a three way call can answer all those questions and take care of a bunch of stuff in one phone call, it could also create a situation where your renter feels like you are not letting him/her take advantage of all the options. Saying to your renter up front "I won't waitlist for you" and having MS make the offer and then having to say "no, we won't waitlist" - the second is more awkward.
ETA: I don't mean to say this can't work, its just one of those situations where you need to know yourself. If you are the type of person not to stand your ground, a MS/renter conference call may have you doing things you don't want to do. If you are the type to want to be nice (and then kick yourself for it), you may "give" more than you want. And if you don't understand the options MS may present to you and your renter, and what they mean for your contract, well enough to make snap decisions, you may make the wrong decision.