The answer is NO. Elastic Beanstalk only supports a single key pair. But you can manually add ssh keys to authorized_keys file, but the keys which are added will not be known or access by Elastic Beanstalk tools.
You can create a file named .ebextensions/authorized_key.config is also a way to do it.
ssh-rsa AAAB3N...QcGskx key_name
ssh-rsa BBRdt5...LguTtp another_key
The name of file authorized_keys.config is arbitrary.