if you want to use rtmedia for UM

function.php

//@see http://community.rtcamp.com/t/permalinks-with-ultimate-member/4778
//if you want to use rtmedia for UM

add_filter( 'author_link', 'rtmedia_for_um', 10, 3);
function rtmedia_for_um($link, $author_id, $author_nicename) {

	if ( class_exists('UM_API') ) 
		$link = str_replace('author', 'user', $link); 
		// get_author_posts_url: http://yoursite.com/author/user-name/ to http://yoursite.com/user/user-name/

    	return $link;
}