Unfortunately, no. This is something that I want to change, but when Feed Digest was first designed (over 2 years ago now), for reasons of efficiency only one type of "description" field was to be pulled out of any feed items. There's a hierarchy for this, so if description is missing, then it'll use content:encoded.. but currently I think description is higher in the hierarchy.. so it'll prefer to use description if it's present.
In theory this should probably be the other way around, but it's not something I want to change in the existing version due to the tens of thousands of established digests that are expecting it to work as it has done.
The idea for the future is to merely keep verbatim copies of what's in a feed, and then let you use the special tags to specifically choose what you want to show.. but currently it doesn't work like that and mushes everything down to an efficient, but less dynamic, processed version of items.