"Give back" is a tricky subject. I give a discounted rate to customers who are willing to open-source any re-usable aspects of the solution I develop for them. I find that approach is not understood by most corporations, though.
Based on the details @@bluehash has provided I think a small (~ 5$) fixed-price fee for any solicitation is a reasonable solution: making the solicitor have "skin in the game" should reduce the spam considerably. I'd hope the micropayment infrastructure would not be a huge impediment. A "free if the result is made public" policy is probably too complex to work.
Given how 43oh collects postings across a couple microcontroller lines including Tiva and STM stuff, I think postings for pay or barter-compensated contract projects involving microcontroller hardware or software development would be appropriate, even if they aren't MSP430-specific (sometimes an MSP430 may not be the right solution). I don't see a clear need to support searches for new employees, since those have a well-developed Internet infrastructure.
A fee to advertize for opportunities with value exceeding some limit ($10K?) makes sense, but without the limit would probably drive off somebody who wants to do an in-kind expertise or hardware swap that would otherwise fit 43oh's culture well. Though perhaps not enforceable, I'd also prefer to see requests only from principals (those who want the work done), not from head-hunters, or at least require mediated offers to be clearly labelled since they affect the contract value.