They’d be just as successful as all the NRL players who have gone over to the NFL mid career. And the ones who don’t make it, have other leagues to play in that still earn them big dollars.
The only way I can see it happening is if we could somehow convince them to come over as 17-18 year olds to give them time to learn the game. But at that age they haven’t yet failed to make it in the NFL.
Maybe look to pilfer rugby sevens teams from around the world? Plenty of quality athletes like Miller who probably have some background in playing rugby league, or at least have less of a learning curve compared to an NFL player.