Answered via a support ticket - posting resolution for those that happen across this post :)
As to the question at hand, note that you can bind RadDataEntry at design time by setting its DataSource property.
It will automatically generate default editors. You are free to replace
a specific editor with a new control by dragging the desired control
from the Toolbox and dropping it onto the PanelContainer inside the RadDataEntry.
However, you need to match the new editor with the corresponding
property. If you look at the designer file you will notice that the
automatically generated editors use simple data-binding for managing the respective property coming from the DataSource. You can follow similar approach. Here is an example how to bind a RadMaskedEditBox to the Phone property of a customer:
this.radMaskedEditBox1.DataBindings.Add("Text", this.customersBindingSource, "Phone", true, DataSourceUpdateMode.OnPropertyChanged );