Can one (who is not strict about cholov Israel) eat Dunkin' Donuts without a kosher certificate?
About ten years ago, I learned the following, specifically about Dunkin Donuts (DD), from Rabbi Gershon Segal, a local rabbi who does local supervision, including of local DD branches, on behalf of local and national kashrut agencies. This is from my memory of what he said verbally back then, so contemporary reality in various locations may vary. However, I think this information is sufficient to indicate that you can't just assume that all DD are kosher without reliable inside information.
No, DD in outlets that are not under kosher supervision are not OK to eat. One issue is the provenance of the shortening. All of the branches use the same recipe to make the donuts, with all the same ingredients. However, you can have the same ingredient come in kosher and non-kosher versions.
In the region that Rabbi Segal works in, all DD branches get their shortening, in packages produced specifically for DD, from a certain factory. That factory produces shortening on two different production lines, one of which is dedicated to shortening, and the other of which is shared between shortening and lard. Shortening produced on the former line is certified kosher, while shortening produced on the latter line is halachically considered to contain pork residue and is therefore not kosher. The factory thus produces two versions of its shortening packages, with the only difference being that one bears a notice of kosher supervision, while the other doesn't. One of the things that kosher-certified DD outlets do differently from non-certified outlets is that they [certifiably] only use the kosher shortening. So, there is a real chance that the donuts in the other branches are actually not kosher, even though they are made with the same recipe.
Why would you assume it's acceptable? Most Dunkin Donuts chains have sausage items that could very well have been produced on similar equipment.