The answer is.. it depends. Generally yes, but we can only show what we have received. Many feed providers only put content excerpts into their feeds as a way to encourage people to click through to their sites. If that is the case, we can only show the excerpt. If the whole article has been provided, however, you can edit your template to show this instead.
In your control panel you can edit your digest, and at the bottom where you choose the template there's an option to edit your template 'manually'. When you do this you see the 'guts' of your template. There'll be a bit that looks something like %DESCRIPTIONPLAIN,100% for example. This means it'll show the item's description trimmed to 100 characters. Change that 100 to a higher number, or just use %DESCRIPTIONPLAIN% to show -everything- we have for each item :)