Hello Riley, firstly a warm welcome to Nimble and Nimble Connect.
It's possible to route iSCSI networks but personally I wouldn't do it.
Within a Nimble system you had two options to replicate your data; over your management network or your iSCSI data network. Most customers chose to replicate over management.
With Nimble as long as you're on NimbleOS 2.1 you can create separate subnets for different requirements, which means you can create a dedicated Replication Subnet if you so wish.
This blog post might shed some light and give you some ideas in order to facilitate replication over your private WAN link: Nimble OS 2.1 Part 7: VLAN Tagging Support