Displays the list of attendees when on single event page of WordPress plugins "Events Manager". This trick requires BuddyPress to run.

events-manager-trick.php

<?php

/**
* Script to copy in your activated theme functions.php for instance 
* Make sure BuddyPress and Events Manager are activated on your blog before using this trick
*/

// beginning of the code to copy paste
function imath_displays_confirmed_attendees( $output = '', $object = false, $target = '' ) {

	if( !function_exists( 'buddypress' ) )
		return $output;

	if( empty( $output ) || empty( $object ) )
		return $output;

	$attendees = $object->get_bookings();

	if( !is_array( $attendees->bookings ) || count( $attendees->bookings ) < 1 )
		return $output;

	$new_output = '<div id="attendees"><h3>Ils viennent !</h3><ul>';
	$list_confirmed = array();

	foreach( $attendees->bookings as $attendee ) {
		if( !empty( $attendee->booking_status ) && !empty( $attendee->person_id ) ) {
			$list_confirmed[] = $attendee->person_id;
			$new_output .= '<li><a href="'.bp_core_get_user_domain( $attendee->person_id ).'">' . bp_core_fetch_avatar( array( 'item_id' => $attendee->person_id, 'object' => 'user', 'type' => 'thumb') ) . ' '. bp_core_get_user_displayname( $attendee->person_id ) .'</a></li>';
		}
	}

	if( !empty( $list_confirmed ) )
		$output .= $new_output . '</ul></div>';
	
	return $output;
	
}

add_filter( 'em_event_output_single', 'imath_displays_confirmed_attendees', 10, 3 );
// end of the code to copy paste

Same question as @winstart ! this is exactly what I have been looking for for several days !