Can I use another schematic capture program and generate a netlist which SuperPCB will import?

Yes, you can use a number of other schematic editors with SuperPCB. These include OrCAD, Tango, Electronics Workbench, and others. You need to produce a file either in Tango format or SPICE format. In these formats, the netlist can be converted to SuperPCB format using the NETIN utility which comes with SuperPCB (MA85100/MA85000 versions).