Using a fairly fresh install of SaltStack on an EC2 image.

/etc/salt/cloud.providers.d/ec2.conf reads:

providers:
  dev:
    provider: ec2
    minion:
      master: 10.185.216.72
    ssh_interface: private_ips
    id: "..."
    key: "..."
    private_key: /etc/salt/dev-app-east.pem
    keyname: dev-app-east
    securitygroup: dev
    location: us-east-1
    availability_zone: us-east-1a
    ssh_username: ubuntu

/etc/salt/cloud.profiles.d/ec2.conf reads:

base_ec2_box:
  provider: dev
  image: ami-c30360aa
  size: Micro Instance
  ssh_username: ubuntu

Creating an instance results in:

# salt-cloud -p base_ec2_box  test.example.com
[WARNING ] The function 'cloud_config()' defined in '/usr/lib/python2.7/dist-packages/saltcloud/config.py' is not yet using the new 'default_path' argument to `salt.config.load_config()`. As such, the 'SALT_CLOUD_CONFIG' environment variable will be ignored
[WARNING ] The function 'cloud_providers_config()' defined in '/usr/lib/python2.7/dist-packages/saltcloud/config.py' is not yet using the new 'default_path' argument to `salt.config.load_config()`. As such, the 'SALT_CLOUD_PROVIDERS_CONFIG' environment variable will be ignored
Usage: salt-cloud

salt-cloud: error: There's at least one cloud driver details under the 'providers' cloud provider alias which does not have the required 'provider' setting