That's a bit odd phrasing, that has guilt undertone. Individuals are unlikely using open source for personal financial gain, but somehow this sounds like they actually "owe" something, kind of shifting the blame from corporations that are actually making money with open source software and often not paying contributors anything.
Also hiring someone to contribute to open source, makes that person likely represent interest of the corporation rather than the project they will contribute to and these are not always aligned. It also takes time of maintainers to actually review and gauge value and viability of the contribution rather than actually spending time on development of the project.
I think much better idea to "contribute back" is to actually pay the existing contributors rather than having own pet one.