The DOI field in Data Set content is a text field not a link field type. With Dispaly Suite Fields one can add a code field that will linked the DOI to doi.org.
The trick here is to use tokens to display the DOI and to link to.
So: Administration -> Structure -> Display Suite-> Fields and Add a code field.
Give it a Label and check Entities-> Node and at the bottom check Tokens
The token for the DOI field is: [node:field_doi]. You can browse the available tokens to find all the available tokens.
With text Format set to Filtered HTML you can put something like the text in the image below in the Field Code, where the link of the token field is: doi.org/[node:field_doi]
The only task left is to enable the field in the Manage Display of Data Set and drag it to where you want it to appear.
Display Suite Fields are very handy for adding other fields which can be blocks (use views to define a block)