There is not a document with specified compatibility.  Isilon communicates with external systems via standard protocols such as NFS, SMB, etc.  Therefore any external system that is capable of communicating to a network using standard protocols will be compatible with Isilon.  If you are seeing a performance variation between systems, I would look into the networking differences between the two.   Connecting over 1Gb or 10Gb link? 1500 MTU or 9000 MTU? Could there be a MTU mismatch? What SMB or NFS version is the client speaking?  You want to approach your performance troubleshooting from a networking perspective and see if you can narrow down the issue.  Take the application out of the picture, and just ping between client and cluster.  Are you getting latency in the basic signal request?
i am testing the Customer's environment now, i can see very good results with specific Servers and really bad results with others, however, they are all connected the same way, but HBAs are different, OS versions are different, Host Software Versions are different  so i tried looking for a Compatibility matrix for Isilon with HBAs, Software, etc.. couldn't find any,  is there any document discussing this?
is there a preference for HBA versions or modules for Isilon?