I haven't come across a UX term for this, but a roughly taxonomic approach, from general to specific, is:
A general term for these strategies, used in game theory and behavioral economics is cooperation.
You are describing a cooperative situation where mutual benefit arises from cooperation, but the user has to give up something (privacy) with a known or unknown delay to getting something back (information). Because the users all undertake the same actions (agree to disclose), these strategies can be described by tit for tat or reciprocal altruism.
For your specific case, you're describing the disclosure of information for mutual benefit. This is similar to the mechanics of mutual nondisclosure agreements in business where two or more parties agree to share potentially compromising information for mutual benefit.
It may be helpful to distinguish between: 1. bilateral advantage, where two parties each gain benefit from disclosure, and 2. direct network advantage where disclosure by every additional party brings advantages to all other cooperating parties. For example, members of social dating sites share personal data but benefit from the data of not one but many cooperating people.
I think the terminology above is only really useful for background reading. For working purposes the term I would use is cooperative disclosure, because this properly captures the aspects of cooperative strategy and information disclosure for this situation. An alternative, for social networks, is social disclosure or cooperative social disclosure.