Maybe, but I see it more like this
Hard workers will work for no money, for a little money, or for a lot of money. A lot of them actually pay money to work, which is sort of crazy. They always work. Workers work. They'd go nuts, otherwise.
People pay them money to get them to work on THEIR project and not some other guy's project. If they pay them too much less than the other guy would, they might eventually lose their worker, and that's the risk they accept by underpaying.
Likewise, if an employer (or grant-provider) sees someone working for no money or low money, he is likely to make him an offer, so that he can influence what that worker is working on. So, I think what FOSS does, that is positive, is make hard-workers working for no money, or who are temporarily unemployed, more visible to potential employers.
And you can't fake that by just slapping something together on GitHub and running off. Employers can literally watch you work in real time.