I'm answering my own post here but I found out the solution myself.
Turns out, enabling BMC lan on an S3200SH board requires that you connect the LAN port with the two USB ports to the network as this is the assigned port for BMC lan access. That' all.
Is the solution I found documented in the docs for this board? I've rummaged through a lot trying to understand ad seek answers to this problem and found none in the intel docs telling me to use the port with the 2 USBs if you will need to access the BMC over lan.