Brad, I'd take a frag no problem, but it has more to do with my attitude towards reefkeeping than any rules about pests. You're never going to get a sterile piece of LR, so it's a pretty good bet that sooner or later something undesirable is going to end up in your tank, no matter what precautions you take.
The best approach, IMO, is to observe whatever shows up in your tank and learn about it - what it eats, what kills it, what makes it multiply, ect.
The ocean isn't overrun with flatworms or red bugs, so if our systems are, we need to figure out how the limitations of our reef setups are allowing that to happen.
(I'm sure that helps you a lot........
)
Mitch