Writing REU Recommendation: Should I mention the student is an underserved demographic? I've not written an REU recommendation letter before, and I'm wondering what is or isn't appropriate to mention regarding demographics, and what might or might not be in the student's favor to mention.

1a) I know that NSF's broader impact criterion looks favorably on increasing the participation of under-represented groups at the graduate student and faculty level. Do REU sites get any kind of credit from the NSF for accepting underserved demographics? Is this credit meaningful?

1b) If it is meaningful, is it appropriate to point out that a student falls into an under-represented category? I know that there is a great amount of sensitivity to certain demographics questions, as well as a strong preference for self reporting. Also, if this is something that REUs tend to ask in their application process I don't want to reiterate something obvious.

2a) My current institution does some undergraduate research but does not have masters or PhD students. Thus, an REU experience is especially beneficial to our students who have not been exposed to the larger academic research enterprise (particularly if they're considering grad school). As previously, do REU sites get any credit for accepting this kind of student (possibly under the theory of promoting research infrastructure)?

2b) If this is meaningful, is it appropriate to mention? I'm concerned that doing so might raise a great big red flag pointing out that this applicant is a total novice.

3) Lastly, should I mention that this student has said they're seriously considering graduate school? I would think this would be a clear positive statement for the recommendation, since (if the student turns out good) the REU institution will have a good shot at recruiting them. But, I've never been on the admissions end of this process. 

All these questions are in the context of a good student who I can write an otherwise strong recommendation for, and are certainly not the basis for a recommendation. If included, these would go in a miscellaneous paragraph that says things like "works well with others".
As has been said in the comments before,

1.a) Most REU specifically say they encourage underrepresented minority students to apply. I understand some of the grants the NSF gives out require that the research group be diverse.

1.b) However the REU application the student must fill out already contains a question regarding this subject, and as @Tom Church pointed out, the student is not obliged to disclose this information. So I would say you should not mention it in the letter

2.a) Again, most REU's specifically encourage this type of students to apply,

2.b) However it is something the student should mention in the personal statement, so again it would not be your place to mention.

3) Yes, you and the student should mention his/her interest in graduate school, as again this is something REU's look for.