Does anyone know the regulation that covers the National Guard recruitment Initiative called "Simultaneous Membership Program" ?

If you search the forums here you will find lots of information about the SMP

OK, the recruiter is being generally straight with your son on how things work. If he enlists in the Guard and gets MOS qualified, he is exempt from the first two years of ROTC, can collect GI Bill, most states offer additional educational benefits like tuition, and he get paid for attending Drill. He would then contract as a non scholarship student to ROTC his junior year, then sign up for the SMP program. It offers several benefits, he would get paid as an E-5 for attending drill, he can gain up leadership experience outside of a school environment and he doesn't lose any TIS and would commission as 2LT Prior Service, which is better pay again. The only downside is that you compete with everyone else in the class for the available active duty slots and while you will fill out a wish list of Branches, the active side is needs of the Army just like OCS.

It's been a long time since I was S1, don't know the answer to the last question.

Looks like others have already given the regulatory guidance. I'll just chime in to say that I did SMP way back in the day, and believe it was one of the best decisions I ever made. Mine was a bit different in that i joined ROTC first and then the SMP program in my Junior year. Still, it made the academics of ROTC a lot more immediately/obviously relevant. It was also a fairly low stress OJT experience.