I assume you've looked at the documentation on InfoSight which unfortunatley doesn't cover every possible configuration as you've found.
The following is designed as a getting started guide which may help explain some of the terminology: http://uploads.nimblestorage.com/wp-content/uploads/2015/05/22100349/nimblestorage-smartstack-getting-started-guide.pdf
Although it does reference the topology you appear to have it tells you to ask for help , so I have what I believe you need based on the information you provided above. If you have multiple iSCSI subnets then this would be done differently.
From what you have said above you need the following:
Connectivity to one or more upstream access switches. (Single iSCSI VLAN)
The Nimble array can be connected to one or more upstream switches. The upstream switch (Nexus 5K in the below example) will need to configure the connections to the Nimble array as non-tagged access ports. The connectivity from the UCS FIs to the Nexus 5K can be of type “Network Port” or “Upstream Port” with a native VLAN set to the iSCSI VLAN. Note that if desired you can additionally use UCS pinning to specify which path to a given FI a host will take. This is a legacy mechanism for MPIO traffic, but will work when you have a single subnet for iSCSI connectivity. Note: using UCS interface pinning is not a substitute for host based MPIO requirements.
I would recommend you speak to your SmartStack Partner to assist further with any configuration work.
This probably does not help much but we recently installed a UCS Mini system. This is the network layout that we ended up with:
We have a single 10GB switch that we wanted to use (I think similar to your setup) I think we were able to make it work temporary while we transitioned off of our old servers. but in the end it was easier for us to directly attach to the UCS Mini. I would think you would need two switches if you wanted to maintain redundancy?
Nimble has a few different documents on configuration, however since I am new to the UCS world I ended up using parts of all of the documents to piece things together. I could not find one document that covered every from start to finish. I I can help please let me know. (I am no expert on UCS or Nimble, but our system seems to be running pretty well the way it is configured.