Hello Matthew Shaw,
I just noticed the below wiki link for reposcan / RDT, it lists all the other necessary switches but it is still missing to list the -dbkey under "List of options is" when it is BI4.0
http://wiki.scn.sap.com/wiki/pages/viewpage.action?pageId=143065487
Although, the reference to official documents for reposcan of each version also exist; however, a small explanation for the -dbkey under "List of options is" can be specified so when people see the wiki, it is easy to refer -dbkey than running through pdf and reaching page number 11 of the below doc:
this mandatory switch in BI4.0, is often forgotten - It will help readers to identify easily as to what they were missing while running reposcan for BI4.0 while they didn't miss when it was XI3.1
It is just my suggestion and sorry I couldn't comment this on the wiki itself as it didn't allow me and it keeps on saying "Loading the editor" forever.
I hope it helps others as well.
Thank you, Rahul