Is autocompletetype limited to the types listed? How do I add AutoCompleteType="UnitOfMeasure" and link it to my db? I'm trying to avoid using the combo box.
Creating new AutoComplete values and linking them to your database is not possible. Take a look at this MSDN article, which describes how AutoComplete is implemented. Basically, AutoComplete information is stored by the browser in a vCard, which is encrypted and stored on the user's computer and is inaccessible to web sites. Since the browser uses a vCard to store the values, you are limited to using the available fields in a vCard when specifying how to categorize your form's inputs. The enum used to select the AutoCompleteType in the RadTextBox contains the common vCard fields.
I do not think AutoComplete was ever meant as a way to replace the combo box.