If I remember correctly (I was not involved in the interactions), DAR said they did not want Wikitree to deeplink to specific records on their website (I don't know why). If that is the case, an external link template would not be appropriate here, because the only link it could add would be a link to the DAR homepage.
The DAR Source template was created to appease DAR. It appears that it may be impossible to both (1) appease DAR and (2) maintain strict enforcement of the Wikitree rule against Source templates.
Options appear to include (1) seeing if DAR has softened or will soften its policy on links (given the time and effort that was expended to get approval for the current template, I don't believe that this will be a popular idea with anyone who was invoved), (2) acknowledge that the DAR template is an exception to the general policy against Source templates (I think this is entirely justified; for one thing, the template was created and approved before the policy existed because of the need to satisfy DAR), and (3) call the template an External Link template, even if it isn't one.
Edited: The current template does in fact include an external link to the record for the patriot, not merely their name and database number. But it does include more content than just a link.