Depends on what you mean by "end game content," but getting into pretty much anything as an RDM is perfectly fine. Their biggest advantage is during progression on Extreme/Savage tier content, where their on-demand rez capabilities are incredibly helpful; this is less so once you've cleared and everyone is presumably on top of their game, but they're not incapable of clearing or anything. The major disadvantage they have is more that they don't bring anything to the table that BLM and SMN already do, and that's only really when it comes to meta comps. That being said, this only matters at Savage-tier or higher content; everything else, no one cares what job you are, and even at that tier personal skill trumps meta rankings. RDM is also pretty easy to pick up, so if it sounds fun, give it a whirl.

I admittedly may be a little biased as an RDM main myself, but there you go.