You can stick the BX-P-ECOMLT on a different sub-net, and basically have the on-board Ethernet port be an isolated network with your BX-EBC100-M on it.
However, there is no Ethernet "bridging" functionality available (i.e. be able to see devices on a different subnet that is connected to the on-board via the POM network).
If they were all on the same subnet, both physically and address-wise, you can see everything. But I don't think that's what you are wanting.