Yes, this is exactly what the "Guest Member" check box is for on the Members screen. You can enter all this persons information just like there were a member of your own team but they are marked as a guest. Once a member is a guest in your account you can check them in/out of a mission just like normal (non-guest) members.
You can't message guest members in the Message screen, Guests are filtered out by design. If you entered a guest members contact information you will need to contact them manually.