Does partnering with institutions that don’t offer graduate degrees meet NSF's broader impact criteria to work with “underrepresented groups”? A way to fulfill the broader impacts requirement of the NSF merit criteria is to integrate groups that are historically underrepresented in STEM fields into your research and outreach.  (I’ve listed the most frequently referenced groups below).  NSF indicates that one way to practically achieve this goal is to partner with academic and other organizations that serve these groups, i.e., by  “reaching out to Institutions with diverse research and instructional goals and practices, including community colleges, minority serving institutions, women’s colleges, and institutions for people with disabilities. “  

In older literature circa 2008 there are also references to a role for partnering with “non-Ph.D.-granting institutions”, likely b/c schools that don’t offer advanced degrees give their students less exposure to advanced STEM research, and also can't expose students to the dynamics of graduate study.  

I’m wondering if NSF has phased out this emphasis on collaboration with teaching-focused college or if it still exists.

Specific Underrepresented groups mentioned in NSF literature


Alaska Natives, Native Americans 
Blacks or African Americans 
Hispanics 
Native Hawaiians, Other Pacific Islanders 
Persons with Disabilities 


Misc Notes:


There is evidence that Broader impacts related to underrepresented groups are one of the least common types of activities proposed: [How broad are our broader impacts? An analysis of the National Science Foundation's Ecosystem Studies Program and the Broader Impacts requirement].  (http://onlinelibrary.wiley.com/doi/10.1890/110106/abstract).  
Blog commentary on the above paper:Broader impacts ≠ reaching underrepresented groups
An interesting blog post on how students from smaller college might be disadvantaged when competing for NSF pre-doctoral fellowships: "NSF Graduate Fellowships are a part of the problem"
I think the reason we want to increase representation of underrepresented groups is that they have the inherent potential for higher representation and achievement and just need some help getting going.

You can't say


  I decided to do recruit theatre majors to our math PhD program, because theatre majors are underrepresented in our program compared to math and science majors.


Theatre majors don't, as such, have inherent potential to do well in math. (Or if they do, some other example will serve to illustrate the point.)

So you'd want to make the case (or have the case already be clear*) that the institution not offering a graduate degree was serving students with inherent potential to do better.

*Regarding that, see @ElizabethHenning's comment below.