The questions I proposed above were gauche semi-serious examples. There are probably a number of more subtle questions that would correlate strongly with self-esteem without setting off alarm bells in the people that answer them.

This isn't something that requires alarm bells. This is a dating website. Full signalling and screening mode is activated as a matter of course. It is extremely unlikely that I could benefit from giving the system evidence that I have low self esteem so I am not going to do so unless all else is compellingly not equal. I suppose this also requires being able to judge what questions have what self-esteem connotations but that isn't too hard.

It occurs to me that I play OkCupid as a min-maxing munchkin. (I recommend this. It seems to work!)

Part of the reason for me talking about it is how unpalatable and creepy the idea is, and how a lot of the factors surrounding people being attracted to each other are not available to dating website service providers without a lot of effort they're probably not prepared to invest. There are probably some areas they can capitalise upon, however.

I don't find it especially creepy. Sounds useful. I want the website to take whatever information I give it and connect me with people in the most effective way possible. Anything I don't want it to know I will not tell it (I will lie to it if necessary).