"Ghouls are immune to most forms of radiation that still remain in the Wasteland. Radiation poisoning cannot get worse for the ghouls, [b][u]though it can hasten the process of decay and lead to their decline into the feral state as described above[/u][/b]. However, many ghouls report feeling healthier when exposed to [b][u]low-level radiation[/u][/b], and thus make their homes near locations with acute background radiation. The ghouls known as "glowing ones" actually enjoy large amounts of radiation, which they describe as being "comfortably warm." They are even healed by it." - Sincerely, verified information.

Jason Bright is a non-feral glowing one likely because he was exposed to just enough radiation to make him a glowing one, but not in such a huge amount that it turned him feral. This was a result of [b][u]low-level radiation[/u][/b], and the glowing ones that [i]do[/i] enjoy higher levels are not regularly experiencing [b][u]2000 Rads per second[/u][/b], they would be more in the realm of 10-15 Rads per second. 

Ghouls are not some magical species of superhuman that can survive every kind of radiation the world throws at them. They are living things, and even if those living things gain an advantage from being in the presence of [i]some[/i] radiation, their organs and nervous systems would be completely destroyed by the levels described in the river.