You can pack the dam with a scraper if you know what you are doing. We have built several with a scraper. They want to you overbuild the dam to account for shrinkage. 15% for a dozer and like 7-8% for a scraper.

If you drive keep driving over the dam with a loaded scraper it would pack it. A loaded scraper weighs a lot more than an empty one.

The scraper would be just as efficient or more efficient than a dozer. We built our latest dam with three scrapers and a dozer. It is a fairly large being 180' wide at the bottom and it is 20' wide at the top. This dam was built over the course of four days. The scrapers packed the dirt nicely but the dirt was a red clay that packs well.