Correct NROTC Form for Drop on Request?

JMPO but I would say yes, since there is a DoR checkbox on it. Perhaps @NavyNOLA or someone else will jump on with an authoritative reply.
No paperwork is required for college programmers not on advanced standing. Just tell them you're done and hand in your gear.
I am still not certain. If you look at Chapter 6-17, Paragraph 2a in the Regulations for Officer Development (ROD), it provides as follows. The ROD is located at M-1533.2A - Regulations for Officer Development (ROD)_2015.pdf

“2. Scholarship (Not Obligated) or College Program Basic

a. When processing a student for disenrollment, the Disenrollment Report, NSTC 1533/122 shall be forwarded to NSTC OD4.”

NSTC 1533/122 is the form in question on whether it applies to a NROTC college program participant who voluntarily Drops on Request (DOR).

The form is located at Student Dissenrollment Recommendation.pdf
Requirements have changed since the last version of the ROD was published. There's nothing for your son to fill out. Just gear return.