This code snippet adds all approved users whose Ultimate Member profiles are public to the sitemap generated by Yoast SEO plugin.

um_wpseo_sitemaps_users.php

<?php 

/**
 * Add all approved users whose Ultimate Member profiles are public to the sitemap.
 */
add_filter( 'wpseo_sitemap_entry', 'um_wpseo_sitemap_entry', 10, 3 );
add_filter( 'wpseo_sitemap_exclude_author', 'um_wpseo_sitemaps_users' );


/**
 * Filter URL entry before it gets added to the sitemap.
 *
 * @param array  $url  Array of URL parts.
 * @param string $type URL type.
 * @param object $user Data object for the URL.
 * @return array
 */
function um_wpseo_sitemap_entry( $url, $type, $user ) {
	if ( 'user' === $type ) {
		$url['loc'] = um_user_profile_url( $user->ID );
	}
	return $url;
}


/**
 * Retrieve users, taking account of all necessary exclusions.
 *
 * @param array $users Array of user objects to filter.
 * @return array
 */
function um_wpseo_sitemaps_users( $users ) {

	if ( get_option( 'blog_public' ) ) {
		$current_page = empty( get_query_var( 'sitemap_n' ) ) ? 1 : (int) get_query_var( 'sitemap_n' );
		$max_entries  = (int) apply_filters( 'wpseo_sitemap_entries_per_page', 1000 );

		$args = array(
			'offset'     => ( ( $current_page - 1 ) * $max_entries ),
			'number'     => $max_entries,
			'meta_query' => array(
				'relation' => 'AND',
				array(
					'key'     => 'account_status',
					'value'   => 'approved',
					'compare' => '=',
				),
				array(
					'relation' => 'OR',
					array(
						'key'     => 'wpseo_noindex_author',
						'value'   => 'on',
						'compare' => '!=',
					),
					array(
						'key'     => 'wpseo_noindex_author',
						'compare' => 'NOT EXISTS',
					),
				),
			),
		);

		$users = get_users( $args );

		foreach ( $users as $i => $user ) {

			/**
			 * Skip users whose profiles can not be indexed by searching engines.
			 * Settings that influence profile indexing by the priority:
			 *  "Search engine visibility" in [wp-admin > Settings > Reading]
			 *  "Profile Privacy" in [Account > Privacy]
			 *  "Avoid indexing my profile by search engines in [Account > Privacy]
			 *  "Avoid indexing profile by search engines" in [wp-admin > Ultimate Member > User Roles > Edit Role]
			 *  "Avoid indexing profile by search engines" in [wp-admin > Ultimate Member > Settings > General > Users]
			 */
			if ( UM()->user()->is_profile_noindex( $user->ID ) ) {
				unset( $users[ $i ] );
			}
		}
	}

	return $users;
}

This gist is a part of the article How to add profiles to sitemap.

Documentation: https://docs.ultimatemember.com/
Support forum: https://wordpress.org/support/plugin/ultimate-member/