he's not providing her with good references or she is getting a bad "vibe" and doesn't want to make the date. At least that what it seems like from your information.
Shouldn't be that tough for an "experienced hobbyist" to get a session with a "top provider". If she has "countless" reviews and they are consistent, he's fishing for information that might not be his business.
Depending on how the situation "feels" to you, you might want to let the provider know what he's up to.
Or you might want to stay out of it completely.
Unusual story.

"What exactly is your concern in scheduling a date with this provider who has countless reviews (my assumption here is that they are overall positive ones), a long reputation, and a strong website (i.e. "everything you need to know")"?

I would also wonder why an experienced hobbyist would complain about screening, unless it is unreasonable.  Given the provider's countless reviews and long reputation, it's unlikely her screening process is unreasonable.  If the hobbyist doesn't like the provider's screening process... he is free to pass on her.

Since this is an "experienced" hobbyist, which I assume means well known in the local community, the usual caution about sharing info about a provider (i.e. concern re LE or an abuser) doesn't seem to apply.

I've had that happen.  

Once I got a PM from a dude about a traveling girl was going to see that day. I skipped his "advice" and had a great time.

Everyone seems to have some drama from someone. Skip and and have fun fucking.

You do not owe him an answer

They don't have to go through a screening process plenty of ladies that don't screen .

or is not willing to send her the information she is asking for.

Perhaps, he PM'd you to get your opinion in an attempt to gauge her trustworthiness  in giving  
her more information for her screening.  

IMO, you should refer him back to the provider in question.

Like this:

Dear experienced hobbyist,
   In my opinion, ________ is a top provider with countless reviews, long reputation, strong website and is okay to see. I found her screening to be appropriate. If you are having a hard time connecting with her I would suggest you contact her to see what can be done, or move on.

Happy Hobbying!

 
In my opinion, it's bad form just to ignore people in a forum that is supposed exist to help each other

If you have seen her, had a good time and feel she is ok let him know and if he is uncomfortable with her screening policies tell him to move on.