Fortunately, MOM provides an Import feature which accepts a particular CSV format, so this was mostly a matter of understanding this format and populating the fields with ubercart's internal representations of the relevant data.
As mentioned here, I would ultimately like to see this module evolve into a generalized order export interface which leverages Drupal's Import/Export API to provide any number of export formats, and to populate them in a less hackish way than my current implementation.
Having said that, if you are using MOM for order fulfillment, this module should work for you as-is. If not, it shouldn't be too hard to extend to a different format simply by replacing the uc_order_export_form_submit function with one that generates whatever you need.
As it stands, this module is far from complete- the interface is very clunky, simply dumping the export data in a big textarea from which you need to cut'n'paste into a text file to feed into MOM. This should be updated within the next few days to a mechanism which initiates a download of a CSV-formatted text file through the browser. Also, there should be a secondary step after the initial export where the admin can confirm that the orders were successfully imported/processed, and have their status updated accordingly.
In the longer-term, I'd like to extract the MOM-specific routines from uc_order_export.module itself, making it extensible to multiple different export formats (at present, three options are provided in the Export Orders page, but they are ignored). Ideally, these would make use of the Import/Export API entity definitions, and implement Import/Export "put" engines to actually generate the CSV/XML/whatever.