yep, that's exactly how it's done. put yourself in their shoes, and ask how would you take an 'out of the blue' email from a prospective student. pretty sure you'd reply, because it's about helping someone out, and more than that, facilitating the transition to grad school. you can also tell the grad students you didn't meet 'hey, i met this and this person from the dept while i was there, but can you also kindly give your input on this concern i have', or similar. i am very certain they will take it normally, as some of them must have received few emails from other students this year, as well as in the past years. if there's a list of students already given in the website, there's no need to contact the POI asking for students' email ids - the POI might actually raise eyebrows when you say such. if you feel odd, you can first email the folks you met while you were there, and ask them to forward the emails to those who you didn't meet. this might make the transaction little more smoother.
and of course, congrats on the acceptances!