Absolutely yes, you can join the U.S. Marine Corps if you have a diploma from a charter school *if* that charter schools is in a traditional setting and is not an online school. The military still hasn't figured out the whole online thing as of yet.
Remember that a charter school is still a public school.
Absolutely No and Maybe! The Marines and all of the other branches are now ranking traditional charter schools to determine if they will be accepted. A traditional charter school will NOT be acceptable if it does not have a Gym.