Page 155 of
Server_Administration_v10.5.pdf says "Mac OS X Server v10.4 servers can be administered using v10.5 server administration tools."
Alas, they cannot; this means there's no way to manage a Leopard and a Tiger system from the same box without screen sharing -- something I and every other Tiger admin would like to do for the upgrade process! More generally, people who have upgraded to Leopard must use screen sharing to manage our Tiger Servers. Let's hope Apple fixes this quickly -- rather than after most of us have slogged through our own upgrades.