Most monocots or grass-like plants appear to be resistant to juglone so you should be able to plant what you like. Chasmanthium latifolium or a Carex species come to mind for your conditions.

Thanks! Chasmanthium latifolium does seem like a good option now that I've looked.

So does that mean needle palms are juglone-tolerant too? Birmingham palmettos? Brazoria palmettos? Yuccas? I mean, I'm not going to plant any of those things on the dam, but it could still be handy to know for future reference. I know dwarf palmettos are juglone-tolerant, though, and they grow deeper underground than most palms; in fact, the grass would mostly be a placeholder while I wait for the dwarf palmettos to spread. I also know river canes (which I again won't be planting on the dam) are juglone-tolerant.