Set a user's bbpress role when importing using the Import Users From CSV Plugin

bbpress_role_is_iu_post_user_import.php

/*
	Add this code to a custom plugin.
*/
function bbpress_role_is_iu_post_user_import( $user_id ) {
	//if you had a column in your import with the role in it, you can grab it from user meta instead of setting it here
	$new_role_forum_role='bbp_participant';
	bbp_set_user_role( $user_id, $new_role_forum_role );
}
add_action( 'is_iu_post_user_import', 'bbpress_role_is_iu_post_user_import');