Hi,
I think FAS2552 has UTA/CNA ports: 4 on each node (8 HA Pair)
As you mentioned these are occupied
Port 1:{e0c|0c} = FC
Port 2:{e0d|0d} = FC
Port 3:{e0e|0e} = Cluster
Port 4:{e0f|0f} = Cluster
Query: RJ45 ports only support 1G?
Yes, that's correct.
Query: would it be possible to use only one interconnect port and the other 2 as data ports?
No, you cannot use 'cluster' ports for any other purpose, they are taken-away for cluster communication (No changes allowed here).
Unless, it has a provision for supported card, you may have to live with 1gb speed.
Thanks!