RX2800 included serial port capability

Customer is winding down use of their compufax setup; it currently runs multiple modems on a DECserver 200.  They are dropping down to a single POTS line and would like to retire the DS200.
I think, from the docs I've found, that the single serial port on an RX2800 is usable as a general purpose port; it isn't OPA0, which is provided via the iLO.
Is that correct?  If so then they can use it for one remaining faxmodem.   If not then we'll have to either spec a serial card for the server, continue using the DS200, or find out what other DECservers are supported by compufax (info request already sent to them); I know the DECserver 700-8 modem control  units were not supported and did not work reliably.
Thanks!