I did this on my son's pond when I cleaned it out and refurbished it. It will work fine.
Just be aware that it will likely be at least a two part process. The first part being piling the cleanout behind the dam while trying best as you can to make it shed water. It will be mucky slimy and not be able to do much with it. Let it set six months to a year, then come back in with a dozer for the grading and shaping.
If you try to do much with while it is still wet muck it will mostly be an exercise in futility. Just spread it out best you can and let it set. It actually likely will not even grow much till exposed to the air for a while. After it ages about a year it will grow grass great.
The new dirt will also be very spongy even after it dries out to begin with. By letting it age, it will firm up and be a lot better to level out to seed to grass. I tried working my son's down pretty quick after it had mostly dried out and the tractor would still make deeper tracks than I wanted to leave in the finished product. After it dries out, is spread out with the dozer, and worked down with a tractor and implement, it eventually will work up really nice. But don't expect to go in and have a finished dam within a couple weeks of starting. Figure about a year later before it can be finished. Just give it time, and it will work nice.
That has been my experience with muck in three ponds I have been involved with cleaning out anyway, for what it is worth.
