Can I upload documents from onedrive to iTunes U?

If you have access to a Mac or PC, you can use the web app, Course Manager, to upload the files:

https://itunesu.itunes.apple.com/coursemanager/

See OneDrive's How-to for instructions on how to get access to your files from your Mac or PC:

https://onedrive.live.com/about/en-us/support/

Finally, I suggest you tell Apple about your issue with the iOS version of iTunes U:

http://www.apple.com/feedback/itunes-u_ios.html

It's strange - You can attach a document from One Drive, iCloud, or Dropbox to a private discussion with a student while using the iTunes U app but you can add something to Materials the same way.