Well in broad spectrum if I say you should mention the way how the Nimble storage is connected to the server either FC or iSCSI also it largely depends on "what the data actually gonna reside as 30TB",I mean to say is it a Database, or File server or mp3 and video?
After this you should really consider the way this 30TB will be accessed? either or LAN or WAN.
if LAN i think iSCSI setup is enough and for WAN you should consider FC. ( I am assuming that you have atleast 1Gbps speed as LAN)
That size of share is probably best done directly via the Windows iSCSI initiator and Nimble Connection Manager for Windows. Since you're also using VMware you do have to make sure your iSCSI VLANs can be presented to guests and routed through your network. Once done you'll have a direct, managed, multipath connection to Nimble that's more aware of path changes (controllers failovers) and can hook into the Windows VSS provider. This is especially useful if you're using Nimble for snapshots for backups and/or replication. 30TB can be easily protected against accidental file loss with NCM and Nimble snapshots and protected against major damage with replication (if you have another Nimble target).
And speaking of snapshots: you shouldn't have issues unless the share is very busy. VSS will have to quiesce the whole volume and the time to do that, snapshot it, and report back is affected by how much is going on. If it's too busy the snapshot will time out or users will see odd, momentary disruptions will their requests are queued as others attempt to finish before the snapshot.
If you aren't able to present your iSCSI network to the guest then RDM is probably the next best, followed by VMDK. I tend to like putting that much data closer to the SAN to eliminate performance or corruption risks.
Hope this helps!
PS - If you go with Windows iSCSI make sure your MTU size is consistent throughout the whole network path from vmxnet3 to Nimble!
I think with 30TB you will run into some problems...
Server 2012 R2 has some restrictions for single volume capacities - https://technet.microsoft.com/en-us/library/dn466522.aspx
Maximum size for VMDK in ESX 5.5 is 62TB.
Are you using one Windows disk volume or multiple?
How are you backing it up? In-guest agent or a hypervisor agent like Veeam?