Do you need SQL Server AAG when using SQL Server FCI/RAID10?
If I have a 2-Node AlwaysOn Automatic Failover Cluster Instance with a shared disk and RAID-5 or RAID-10 to account for a SAN failure with the same setup in a second datacenter with data propagation via SAN Replication, is there a way to benefit from using AAG in this scenario?


That depends, are you worries about any of the following scenarios?


Strict RPO/RTO
Does your SAN support write ordering across multiple LUNs?
OS/SQL Patching issues
Controller level IO corruption
Downtime for Maintenance


If your answer to the above is, "Not worried" then I don't see any reason to use any AlwaysOn technology (FCIs or AGs). If your answer is, "Yes, one or more worry me" then I would consider looking into a set of technologies to meet your specific concerns and scenarios.