There has been much debate regarding gelatin ever since the Achiezer permitted it years ago.
The basic concept is this:
Gelatin does not enhance the taste of the food. Therefore even if it is derived from a non-kosher animal, it is considered kosher for consumption. It is added for texture…
This is similar to the Halacha that states that horns and hooves of a non-kosher animal may actually be combined with kosher meat to deem non-kosher meat Batel. Same concept here. If it doesn’t taste good, it’s not Assur.