The wood is expanding and contracting because of change in humidity. If you can control the humidity, the wood won't move on you, or it will move very little.
If you can control the humidity, ONLY then would I consider installing any hemp or crack filler. If they're 1/8" or smaller, forget it. Just keep the floor clean. Usually, once the humidity is 'constant', the floor can actually be relaid because it won't 'move' any more (or very, VERY little.) The problem with any filler that's used in an environment where the boards will move is that it gets 'compressed' and 'pushed out' eventually. Sorry, but that's Mother Nature.