You sure can try them without doing any harm Huntsman. Won't hurt to try.
I assume you already have the mold. If not, I wouldn't buy one for that purpose. I believe those bullets are designed for a gas check, which is not really what you want for a muzzle loader. You should cast them from pure lead, lube them, and probably use a wad of some sort under them. I've never gotten great accuracy with cast pistol bullets out of my .45 Renegade with the 1:30 twist Green Mountain barrel, but you may have good results. It should be fun to try.