I see that mysql replication can synchronize from sybase, but can sybase replication server write to and read from sybase? I'm trying to figure out a migration path of a big old legacy sybase system lots of little applications to mysql and figure I can move the newer apps sooner than the older ones so I want to be able to use both and have sybase replication do the synchronizing. Is this possible?
No, the Sybase replication server only works between Sybase instances.
Golden Gate software has an excellent solution for real time inter-database replication. You can set it up to bi-replicate, so that changes on each side are propagated.
http://www.goldengate.com
Sybase replication server can replicate between Sybase, MS SQL, Oracle and DB2. It doesn't look like it can do MYSQL.
http://www.sybase.com/products/businesscontinuity/replicationserver/heterogeneousreplication
Sybase Replicaton Server can replicate between Sybase and MySQL. You just need to use the MSSS function class when installing Replication Server.