You can certainly use a different type of lentils if desired, but the biggest different will be with the texture. Red split lentils turn quite mushy after cooking so you don't even notice that they're mixed in with the sweet potato. Canned and cooked green lentils tend to be a bit firmer so they might not break down as much when incorporated in with the sweet potato. All options will work, it's just a matter of the texture you prefer. Canned lentils also tend to be higher in sodium so keep that in mind if watching sodium intake.