Hello Author,
Open CASCADE does not support procedural surfaces, except surface of linear extrusion, revolution and offsets. In addition to support of elementary surfaces the other types are approximated with NURBS.
Have a look at a list of subclasses of Geom_Surface, e.g. in Geom.cdl.
Also you might want to check a few surface modeling techniques at my blog, starting with part1 - http://opencascade.blogspot.ru/2009/10/surface-modeling-part1.html
CAD Exchanger (the project I founded, http://www.cadexchanger.com) does convert ACIS to OCC. Law surfaces and other types (skins, lofts, nets,...) are re-approximated on the fly. You might want to try a free evaluation version to see how your surfaces convert to OCC (by exporting to .brep).
Good luck!
Commenter-1