Hello Matthew,
I've given a look at the document: I don't think it can work with a Cisco Router unless trying to remotize the AUX port.
This kind of device is thought to provide a virtualization over IP of one or more serial connections.
See:
Device servers and terminal servers represent the segment of product also known as serial-to-IP converters, which essentially
allow any device with a serial port to communicate with an application across an IP network.
but serial ports here async serial like RS-232 or RS-485, the usual serial interface on a router is of sync mode follows other standards and what is more important it usually has already an IP address configured on it.
An object like the following:
Product Summary
RAD's RIC-E1 serial interface converter and RIC-T1 serial interface converter offer conversion between E1 or T1 interfaces and standard data communications interfaces, including V.35, X.21, V.36, and RS-530, as well as Fast Ethernet, Ethernet bridge or an IP router. The modular design allows for simple interchanging of the interfaces.
at http://www.rad.com/Article/0,6583,37468-E1_Serial_Interface_or_T1_Serial_Interface_Converter,00.html
This could be a better fit for your needs.
However, I would consider using LAN subifs on the Cisco router before using one of these boxes.
Hope to help
Giuseppe