Yes, you can use both in the sump. Some species of caulerpa are invasive... that would be the bad side. If you keep it in your DT, and don't manage it properly, it can cover everything and be difficult to remove. Besides liking the look of them, their fast growing nature allows them to utilize the nitrates and ammonia that a tank produces quickly. I have no doubt it helps keep my parameters in check.
I also use cheato, as I like to use a bunch of different macros. They don't remove the same amount of organics, they certainly aren't attractive and they throw fragments off everywhere in your tank. But they are very hardy, easy to find and are noninvasive,