I've moved your thread from the New Users forum to the Sybase forum. It should get both more answers and more appropriate answers in the Sybase forum.
Different SANs have different degrees of integration with database engines. I've seen every level of support from unusable to poor. I've seen a total of just under 200 SAN based replication configurations. One was successful and one was marginal.
Timing is usually the biggest problem with SAN replication where databases are concerned. Think about what would happen with a simple uni-directional replication scenario if the synchronization between your Sybase data and log devices gets "out of sync" so that one is seconds or hours ahead of the other. Now imagine the fun when that replication becomes bi-directional! When looking at replication, uptime is usually the primary motivation, so mix in a SQL cluster for good measure. I'll wait while you go have a drink or two to calm down again.
If you decide to pursue the idea, make sure that you get the SAN replication folks to demonstrate how this works in your environment. It is relatively easy to make things work in a lab. The real world provides additional amusements which are often overlooked or ignored by sales people!
As SAN and database replication architectures evolve, I'm sure that sooner or later someone will get it right. For now even in light of the expense and extra support effort needed, I'd recommend staying with Sybase replication.
In theory, theory and practice are identical. In practice, theory and practice are unrelated.