Both answers are correct.
AFROTC HQ will remit only tuition. That is it, if it is above the 18K you pay, if it is below, you do not get to place the difference towards room and board.
Some colleges, do give a break on the cost, but some schools also give merit based on the condition you are in ROTC.
It is really important to understand this, because come 2 yrs from now, SFT EA will be a factor for you financially. If you are not selected, the scholarship will go away, and even if the college gives a reduced rate for room and board because you are a cadet, that will go away too. How will you pay for the next 2 yrs?
Also, check into the housing situation at your college. Out of every college our 3 children applied to, only 2 guaranteed on campus housing for all 4 yrs. Most did not guarantee after freshman yr. That means you will have to pony up money for 2 to 3 yrs. Off campus apts vary college by college. DS1 has lived off campus since jr yr., and it costs us 750 a month in rent/utilities, contract is for 12 months, even though he doesn't live there during the summer. DD was forced to move off as a soph, but it costs us 400 a month, for 12 months, again the apt will be empty May-Aug, but we will still owe 400 a month. Both could buy the food plan, but it is unrealistic to believe that you will eat on campus, when you live off campus, so you need to place that into the equation too.
This is the problem for many that accept scholarships, they do not think about the long term issues. They do not investigate deep enough regarding fiscal implications. If you are not guaranteed housing after freshman yr, where will you get the money? Some colleges, such as VT, will only guarantee 4 yrs on campus if the student is in ROTC. Again, look into the housing issue.
Personally, most colleges at this point are just starting to tell admitted students their merit money. So this may be a moot point. I would be shocked if the school does not give you merit, especially since it appears you are going IS. I say that because not many private or OOS charge less than 18K for tuition. Additionally, you are a Type 2, 4 yr, which is only awarded to @15-20% of all scholarships. That means you have very good stats.
DS was awarded an AFROTC scholarship, and every single college gave him merit. It varied in the amount, but he still was awarded merit from each.