I have an entire neighborhood mapped with Civil3D based on a 1955 survey.
Is there any workflow for importing the linework into OHM, or do I have to trace it?
OHM uses the same data format as OpenStreetMap. If you can find a tool or workflow that’ll convert from .dwg to a format such as .osm or shapefile, you can open that converted file in JOSM and upload it to OHM. This Stack Exchange answer suggests going through ogr2osm, but there may be other approaches. Please let us know what you find so we can document it on the wiki.
Before uploading, you’ll probably have to clean up the tags on each feature to match OSM/OHM tagging standards. If you’re unsure about this step, feel free to post a sample of the keys and values here so that we can double-check it together.