Is replication from EqualLogic 6510 to EMC Clariion CX series possible

Nothing that I know of out of the box would support this. There maybe some third party software our there that would allow you to replication between two different storage products, but I am not sure how that would look or work. What type of data are you trying to replicate?

"Is replication from iSCSI EqualLogic 6510 to EMC FC Clariion CX series possible?"

SanMelody could do this... It's fairly inexpensive if you don't have to much storage. Basically you will have to create a virtualized storage cloud to do it which has all sorts cool added functionality.