Been noticing lots of normal provider (ie not bdsm or similar) ads here and elsewhere that say "fetish friendly". Given there are an infinite number of fetishes (just see the reviews here) are these ads talking about something specific?

This term can be more marketing than anything else.  I've seen it mean the lady will keep her high heals on, to wearing certain outfits, to role playing, and yes, perhaps kinkier types of activities.  Overall, to me it indicates a willingness on the ladies part to go beyond a generic session.  This is an area where reviews are helpful, or else you will have to ask the lady what she permits or allows as a fetish.

or inflicting pain, usually with either a whip, lash, or riding crop.  Spanking is also common.

Will entertain some, but not all, fetishes.  You have to ask if she does your specific fetish.  The danger here is that someone desperate for money is going to be tempted to say "Yes" to something they have never done before, and may not know how to do it safely.  If you're into fetishes, you are better off to skip providers that are trying to be everything to everybody (which is why I also eschew CMT's offering full service and trying to be both hooker and masseuse), and book an experienced Domme with a website that lists the activities she normally allows.  If you're going to have jumper cables hooked up to your nuts, you want to be sure you can still have children someday.    

-Sploshing
-Podophilia (Foot Fetish)
-Knismolagnia
-Katoptronophilia (in front of mirrors)

.... some are upfront with what those things are and others are probably just willing to discuss with you in private.

Please translate to English.

supposed to make things easy.