You wouldn't be able to use a 4 cell LiFePO4,,,the DNA 200 has a 3 cell balancing charger. Not 1s, 2s, 4s, etc. Only 3s will work.
EDIT: So basically, if you want to use LiFePO4 cells, you're going to have to deal with a low battery warning constantly and terrible battery life. LiFePO4 cells do have a very flat discharge curve, but they do drop down to 3.3 (or 9.9 for our uses) pretty quick, where they stay for a while before going down below that. So you really wouldn't get the full mAh out of your LiFeP04 unless you could somehow tell the board that it is indeed a pack with lower operating voltage so it would know not to cut off until a lower voltage.