I'm an end-user doing a Sepasoft MES implementation on top of Ignition.
Most of our CompactLogix PLC's only support the one ethernet port. We're using a NAT device to put the PLC on the plant network. We have no issues with this. Ignition isn't hammering the PLC and everything works great.
The only thing with the NAT is that each machine or line or whatever will eat up 2 addresses. You need a public address for the PLC and one for the NAT. In some cases I use the hardware NAT to move to an intermediate address range, and then I use software NAT in the Stratix switch to NAT again up to the plant network. It works fine an and the IT guys don't freak out about using up all the addresses.
I love Ignition and the MES module. We're just getting started, and there is a lot to learn, but the support is fantastic. We're running our line-side andon displays with R-Pi's and they work great. A $50 R-Pi vs. a Win10 box for each installation is going to save a ton of expense.