Firstly, that is a terrible idea. Chuck uses two fighting types, one of which is part water. Larvitar is weak to both of those typings.
Yes, it is possible to enter before Chuck. You just need to pick up the medicine from that island, feed it to amphy, and Baboa will call you ahout the safari zone. None of this requires beating Chuck. However, you should beat Chuck while your there so you can get HM02 Fly.