I agree strongly that the stats are a starting point only for conversing with Hillel leadership about Jewish life.
For "vibrant Jewish life" also look for the academic courses offered. Check the course catalogue under several different departments, starting with "Religion" "Near East Studies" and "Jewish Studies." There might be relevant courses in the History department where the entire course is devoted to the Holocaust, "Golden Age of Spain" etc. See if the courses are taught by the college's own professors or adjunct instructors; figure the college professors are more available to students with office hours, etc.
See if worship services are offered; student-led or clergy-led; and in what denomination (Reform, Conservative, Reconstructionist, Orthodox). Would you consider trying a different movement than one you grew up in? Is there an exchange among nearby campuses to get services more to your liking?
Look in the Student Services section for a "Chaplain" because that might be where the campus rabbi is mentioned. Sometimes Hillel employs a rabbi, who might serve only that campus or several. A college might "have a Hillel" but its students might always be the ones to travel to a bigger Hillel at a different college or uni nearby. That can be interesting, or inconvenient, depending on how you perceive things.
My eldest, who needed financial aid, found much better salary by teaching Religious School at a nearby synagogue and worked there for his "work-study" job. He earned triple the campus rate-of-pay and got a teaching skill that helped him upon graduation as well (NYC actor's day job, no waiting tables
Keep in mind that those percentages are indicative of some but not all of the campus spirit. A student can list him/herself as Jewish but do nothing on campus to identify or contribute, making it "seem" as though there are fewer Jewish students. In big cities, Jewish affiliation rates (joining synagogues) are at 50% of the Jewish population, with higher rates in smaller towns! (need to join to find each other; not so in big metropolitan areas).
I'm thinking that on a campus, you have many students away from homes, families and communities that provided (spoon-fed?) them Jewish opportunities. On campus they have to choose to do this themselves. Some long to get away from it so do 'nothing" on campus except go home for major holidays. Early adult years have the least rates of involvement with religious institutions. Students get back to it when they go to work or begin families. Still you can find Jewish students around you. It's something to think about, how you'll find your own way to express yourself, once away from home.
That said, it's very important, if you care, to see if there is a Hillel organization and how they're doing. Of course the leadership will always paint the best picture to prospective students, hoping for replenishing the leadership! One Hillel leader might say, "If you see an activity that isn't here, you can step up to the plate and start it." which is a whole different message than, "We already have 3 programs that address that.." and there are merits to each.
That said, if you care a lot or even a little, consider that "studies have shown" (unfortunately I can't remember my source on this one, but trust me...) that there are two "tipping points," regardless of total numbers. Under 10% causes kids to feel absolutely alone; the 10% neighborhood feels mighty "thin" if you care about meeting and doing Jewish things; and at 20% you'll feel a vibrant Jewish presence with plenty of other students. At around 20%, you'll feel there are "always more new Jewish kids to meet," instead of "same-o, same-o."
Good luck and it's great to know students include this important criterion in their search.
