giving a bonus, as nominal as it may be, based on healthcare choices? this smells very different than say, giving memberships to a gym to any employee that is interested. i don’t play a lawyer on tv because i am one. and though i’m no expert on this, my instincts tell me you might be accused of breaking the law....appearing to break some law so that an employee sues you costing you a ton of money and time and stress defending yourself
whether you actually are breaking the law is i think, very complicated and would depend on many facts unknown to me
i took a quick look here (below link) and what would concern me is that a person who decides not to be vaccinated could be making that decision based on a medical condition or a religious belief and therefore might be motivated to claim you are discriminating against them based on their disability or religious belief by rewarding others who were able to get the vaccine.....but again, this is a complex fact based analysis and the sort of thing that ultimately works itself out in court when you risk doing what you are suggesting... personally i would try to avoid that
anyway, here’s some good reading that while not exactly on point, is worth being familiar with as a business owner (vaccinations is near the bottom- but all of it is pretty useful info)
https://www.eeoc.gov/wysk/what-you-should-know-about-covid-19-and-ada-rehabilitation-act-and-other-eeo-laws