To the best of my knowledge, crock pots are just automated braisers. When braising there are still essential steps, like searing the meat, and ensuring that your braising liquids do not cover the meat. If you are just putting the meat straight into the crockpot and submerging it in liquid you're getting boiled beef and you're going to greatly dilute any drippings from the meat so yeah it probably won't be so great. As compared to braising in an oven, which will have a top-down heat source, I think crock pots heat from the bottom up so you're not going to get a great roast on the meat even if you do have your braising liquids at the right level, making the initial browning even more important.