Can I use multiple Comar networked receivers to feed data to one display?

The quick answer is yes, as long as your software plotter supports using multiple network data streams this is definitely possible.

To enable this setup you will need to configure the units to send their AIS data stream over different ports, the process for this is covered in this article, so that your display software can see these as separate data sources. Depending on the distance between the locations of your receivers and the reception range you are getting this may lead to the same vessel transmitting to more than one receiver and this would have to be filtered out.