MARSOT doesn't really have anything to do with MARSOC other than being related to USMC selection. MARSOT screener is for MAGTF as 2/C or 3/C, Airborne, Air Assault, USMA CFT, USMA CLDT, Army Mountain Warfare, and USMC Mountain Warfare. It is possible to be assigned to a MARSOC Battalion for MAGTF, but it is by no means assured or even offered from year to year. The MARSOT training opportunities are a recruitment tool for USMC selection. They do not count as a fleet cruise (and MAGTF before 1/C year will not count as a replacement for Leatherneck). Last I checked the MARSOT screener ran from early morning to early afternoon on a Saturday, maybe 7 to 8 hours total. Not comparable to the EOD/SEAL screener, but significantly more intense than Sea Trials.
EOD familiarization training is separate from the 1/C EOD cruise and is offered for 2/C and 3/C. Dive school is a new opportunity for this past summer (or at least had not been offered for the years I'd been at USNA) and was offered to early submarine selects as a recruitment tool. As far as I know selection for those was based on a PST and OOM.
Run a Google search for a PowerPoint titled "2016 Approved PTEs". It is the most recent summer training brief for last summer, given to underclassmen at winter reform.