A much better choice for compatibility yes, but neither Paracheilinus or Cirrhilabrus will pick from the substrate (read: won't do a thing for flatworms).
I did kinda forget that was a stated reason. I don't think that's a great reason to add a wrasse in the first place. Here's my thinking:
If you have flatworms already, there's no way a fish will eradicate them. He might dent the population, at most. There are almost always safe treatments like Flatworm Exit that are 100% more effective. (Apply with care and follow the directions, obviously...people who have trouble goofed in the process somewhere.)
If you don't have flatworms already, then it's a misplaced worry IMO. Likelihood of a flatworm outbreak in a well run tank is very low....many people never ever have a single outbreak - I dare say 99% of people never have one.
Now having said that, there are risk factors that can make some precautions worth taking. To generalize, tanks that are never allowed to stabilize are the ones more at risk. If you are, or will be, someone who is always adding and removing things (livestock, rock, etc...for any reason.) from the tank then you may have reason to worry a little. The long term residents are always going to be at least slightly stressed (therefore susceptible) and there is probably a repeating chance of newly introducing a parasitic organism that wouldn't exist in a stable tank.
By contrast, in a stable heathy environment, almost all our critters - fish, coral, etc - can naturally fight off parasites like these with no effort at all. If you had flatworms in this scenario, you might never even know it.
The only reason I would get a wrasse was because I thought it was awesome and I wanted to take care of it. (And don't hope they won't jump...they will.)
-Matt
Edit: Forgot there's also all the tanks that just stink with wrasses (have many) but have flatworm outbreaks anyway. It really is about a stable, healthy tank.
