Hardware Cluster to VMware, is vMotion an alternative for clustering?
vMotion and clustering aren't alternatives for one another. vMotion moves the same "machine" (albeit virtual) from one physical host to another.

This provides some sort of resilience to hardware failure (unless it's the shared SAN bombing out) but you can't fail over to another host if you would like to create a maintenance window with minimal downtime for example. vMotion won't help you if you need to patch the (virtual) servers without downtime.

If you need the clustering for other things than hardware failure resilience I wouldn't rely on the VMware features but I would create 2 VM's on separate physical boxes and create a regular cluster between the 2 VM's.

vMotion adds a few features like being able to move VM's between hosts to redistribute load and hopefully recover from a hardware failure but is not an alternative for clustering. Clustering between 2 VM's is not different from clustering between 2 physical machines.