Get user role by using user_id in buddypress

Try this function:

function get_user_role($user_id){
    global $wpdb;
    $user = get_userdata( $user_id );
    $capabilities = $user->{$wpdb->prefix . 'capabilities'};
    if ( !isset( $wp_roles ) ){
        $wp_roles = new WP_Roles();
    }
    foreach ( $wp_roles->role_names as $role => $name ) {
        if ( array_key_exists( $role, $capabilities ) ) {
            return $role;
        }
    }
    return false;
}

I’ve not included any exception handling like whether the user exist or not, so you can do it yourself or in case you are getting the user ids list wont even be necessary.