I gave it a test run. First, I added a custom capability to a specific user, using following code
$user = new WP_User( $user_id );
$user->add_cap( 'team_member' );
Luckily, this user can be retrieved using below code, as you suggested
$args = array(
'role' => 'team_member'
get_users( $args );
Which implicitly work like below
$args = ...