Flytraps have no control over what may fall in their traps in the wild! In my experience they can nosh on pretty much any insect, so go ahead and feed your plant pill bugs.
Sorry to contradict Joosa, but whilst sunlight is the number one priority, there's nothing wrong with letting your plant have a good gorge every once in while. Occasionally you may lose a trap to rot, but it's rare if your plant has good air circulation.
With regards to pill bugs, and any insect with a hard exoskeleton in fact, there are always gaps in the armour through which digestive juices can seep, so they can happily dgest such creatures.