I feel like if either of those is true it relies on having an unhealthy animal in the first place where digestion is being interfered with because of something like lack of heat, or imbalance in digestive bacteria due to parasites, or something along those lines. I could be wrong though.
Could all be scaremongering .. I also heard they can cause bloat in some fish ..
Guess the best thing is to feed not too often and feed thawed-frozen