The second, more general use of FidoNet is to refer to any network that uses the FTS technology to pass mail around without being a part of FidoNet itself. AmigaNet is a good example, spanning 3 continents and specializing in only Amiga content.
Out of the box, DLG is equipped to operate in any network that utilizes the FTS technology.
UseNet is a term used loosely to refer to a network of systems exchanging mail in the internet. UUCP is one of many protocols used to transfer news and mail from system to system. DLG comes with a set of UUCP import and export modules. Using free utilities like Matt Dillon's UUCP or the GNU distrbuted Taylor UUCP, you can link your BBS to the internet and offer news and email to your users.
TCP/IP is another popular method of moving mail and files around on the Internet. DLG does not currently directly support this method, though there are a number of third-party utiltiies that do, such as telser.device and telnetd.