No, radon is more an issue in a basement with no air flow, where the gas can accumulate. A greenhouse will have plenty of air flow so radon would be no more an issue than if you were standing outside.
The holy trinity of wholesomeness: Fred Rogers - be kind to others; Steve Irwin - be kind to animals; Bob Ross - be kind to yourself
Ruth Stout was famous for gardening naked. Just like this tiny ad:
montana community seeking 20 people who are gardeners or want to be gardeners