Is there any kind of script that would allow a project with a large number of small repos (for plugins, themes, etc) to import these into ohloh as enlistments?
Ordinarily we discourage users from enlisting a great number of repos within an ohloh project. Be aware that the stability of a project is impacted negatively by the numbers of enlistments it contains and the relationship is not linear; it is more like exponential. Know that any one failed enlistment (no matter how small...) prevents the whole project from completing an update.
With that said, if you are willing to ride herd on a project within those limitations, I know others have done what you are proposing. Some user here should be able to help.
Contact me here if you need additional assistance.