Ultra light tackle and light tackle isn't much different from fly tackle in the size of the lures/flies. I use fly tackle a lot in the surf wading or in the bay mostly from a kayak. Clousers are a lot like Crappie jigs in weight and size. Clousers can catch all kinds of fish.
In the surf, I've caught speckled trout, whiting, bluefish, Spanish mackerel, jacks, ladyfish, and flounder on various flies.
In the bay, it's flounder, drum, redfish, trout, croaker, and sheepshead.
My 4 favorite flies resemble a small shrimp, a small could be crab or shrimp, a mud minnow, and a small baitfish like an anchovy or mullet. Some of the flies I make could be used with spinning reels.
Crappie jigs could work but the hooks are pretty thin wire wise. Any red with any size would be sure to destroy one. Plus, the salt would reduce the hooks to one and done,
Most of what I use is between about 1" 1/2 to about 3" long. It would be very easy to adapt fly patterns to ultralight castable lures. I put little glass rattles in some of my flies, mainly the shrimp fly.
Remember, the fish don't care what is supposed to be for fresh water or salt. I'm a believer if a hunch tells you to try something, do it.