If they used and published a fair algorithm for matching, they wouldn't really be involved in the matching they would just be providing a venue. Similar to a city providing public space for people to meet, like a fair.
Do you think the FBI, NSA, etc doesn't already have access to photos posted on dating sites in the US?
NSA match? Based on your porn search habits, google search history, amazon order history, geographic location, and a social graph based on phone record metadata we recommend you the best possible match.
Even if true, "have access to" is doing a lot of work here. If I had a Borges-style Library of Babel with all the possible books in the world, all configurations of the letters of the alphabet, I would technically "have access to" all human knowledge. But that's very different from having a curated collection which includes specifically only those things, filtered perfectly for you.
Do you think the FBI, NSA, etc doesn't already have access to photos posted on dating sites in the US?