Well I can tell you what I know from working and living with them. One thing is that they are called SARC's (Special Amphibious Reconnaissance Corpmen). Just like all FMF Corpsmen they have to go through all the same initial stuff when becoming a FMF Corpsmen. I'm not sure if they can apply before they graduate or if they have to wait until they get to a unit, but I know that Recon, and now MARSOC units are always hurting for SARC's. After they have passed all of that schooling and are officially FMF Corpsmen they become eligible to attempt the Recon screening/ indoc. They have to meet all of the same criteria as a Marine attempting the indoc. In some cases I know the senior SARC (Senior Chief) might hold them to a higher standard in order for them to come over.
If you prove yourself worthy you'll go to BRC/ ARS, SERE, Jump, Dive, 18D condensed course (were you go to the actuall 18D course minus some things, and do some time in a hospital ER or with an ambulance), and I be leave some type of Dive medicine course. All in all its about a year and a half from start to finish and they usually run them straight through the pipeline.
Like I said I personally am not a SARC and can only tell you what my SARC described to me. Things might have changed as its been about three years but probably not too much. What I can tell you though is that the SARC's I have met have been some of the hardest men I've ever met, just as hard if not harder than the Recon Marines they take care of. They are extremely competent in both combat medical care and unconventional warfare. Hope this helps.