i have halimeda in my tank and it looks awesome... it changes color through out the day from almost white in th morning to a dark green by the time i get home from work. I have a rock that has some wierd calurpa on it almost looks like a bunch of little green mushrooms growing off of runners and some red algae that looks like dragons breath minus the bright trim. I've always been a fan of keeping macro in my reef tanks you just need to keep it under control and remove any that starts to bleach out.
Ive heard it secretes something that is detrimental to coral growth, and i know it uses nutrients (part of the reason i like it in the tank, it seems to out compete other algaes that i dont want and keeps phosphates in check) but all in all ive never had a problem with it. My other love when it comes to aquariums is planted tanks so adding some flora to my sw always seemed like a natural thing to do. The main thing, like everything else in this hobby, is that you stay vigilant and dont let it get out of control, and seriously, keep an eye out for bleached out pieces.