Are you referring to SMO or SMSAP running on Linux? If so, those products do not yet support RHEL 6. For the most part this is due to Oracle not yet supporting Oracle databases on RHEL 6 as of yet.
All supportability info is found in the IMT. If you do not see the config you are looking for, the best way to get an answer on why that may be is either contact your Sales team or use the Feedback ( -> I cannot find my configuration) button within the IMT tool.
IMT stands for Interoperability Matrix Tool. It is available on the NOW site.
In short, you can enter the config details of your host (ex. OS, protocol, HBA), what ONTAP version you are using, etc and then use a feature of the tool called end-to-end views to determine if your config is supported across SAN - SDU - SMO.
There is help available as well as some videos of how to use it should you need them.
So there is not confusion, the product you are referring to as SnapManager for Linux is called SnapDrive for Unix; and yes you are correct, SDU is required in order to run SMO.