Is it possible to connect the Fabric Interconnect from a Cisco UCS 6110/6200 into a Brocade 8510 director as an ISL?
Regarding the interoperability between Cisco and Brocade switchs, Brocade states the following (FAQ3332):
Brocade SAN switches are not interoperable with Cisco SAN switches in native mode.To connect a Cisco switch into an existing Brocade SAN, the Cisco switch must have NPIV mode enabled.To connect a Brocade switch into an existing Cisco SAN, the Brocade switch must be in Access Gateway mode.Cisco states that if you configure their switch to Interop Mode 2 it will allow seamless integration with specific Brocade switches running in their own native mode of operation. Please note that merging a Cisco switch into a Brocade native mode fabric using Interop Mode 2 on the Cisco switch is not a supported configuration by Brocade.
So, it the Cisco Fabric Interconnect can be configured with Interop Mode 2, you should be able to configure an ISL with the Brocade switch. But even if it worked, I recommend you not to use interop mode because, based on my expirience, I have seen more problems that expected when interop mode was used...