I've sort of put off responding to this because I wanted to give everyone ample time to reapond. Disclaimer here, I am not a Recon Marine...just noticing a trend in the questions being asked.
I'd like to preface my response here by asking a question. In relation to your question regarding MART, who cares if they screen or don't screen? Do you want to be a Recon Marine? (I assume yes). Then the answer to your original question doesn't really matter and shouldn't even be on your radar.
I know you're excited and are likely just curious (as we all tend to be when going into something unknown) but really your focus needs to be on what will make you the most successful recruit at PI or SD. Then, what will make you the most successful at SOI. And then, once you're at BRC, what you can do to be successful there. Obviously preperation is a key factor, but knowing who screens who, what the attrition rate is, what kind of packs do they carry, should I wear green or white skivvy shorts....those are things that ultimately will not help you. Even if I told you you're going to the hardest school in the Marine Corps....in the DoD....or in the world....you would still want to go (at least I would hope you would).
My advice to you: focus on preparing your body (properly/safely) and just get down and grind. Chow time to chow time, day to day, weekend to weekend....however you deal with the pain....suck is suck no matter how many Google searches you do or Youtube videos you watch.
Good luck with everything!