I think you'll have a hard time importing from an excel format as I'm not aware of a library to import those. I would also advise against writing directly to the DB as you might miss some constraints expressed in the code only and will miss future ones after that.

Regarding importing them programmatically, there seem to be a few Redmine plugins for that, I can't say how good they work nor if they work with ChiliProject. If you want to develop a script yourself, have a look at script/console which is a console/REPL with the ChiliProject environment loaded so you can test stuff and script/runner which you can use as a shebang for scripts that will run the ruby code in the script in the ChiliProject environment.