No real difference, except duration. If you dry hop in the secondary, you have an exact cutoff. There is some drift in flavors the longer the hops are in the keg, but hops in the keg don't spoil, near as I can tell. I've had hops in a keg for over 8 months without any problems.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
"I would like to die on Mars, just not on impact." Elon Musk