Yuan Yuans are definitely in the Army. The reason you don't see them is probably because Yuan Yuans are either only available (IIRC) in Quapu Khalki and Druze Bayram Security sectorials, or, if you want to make a list using Soldiers of Fortune rule allowing mercs in any army, you need to enable "Mercs" in Army's options. Keep in mind that last time I checked, Army did not account for SWC cost of enabling Soldiers of Fortune in your list. Maybe that has changed. Fat Yuan Yuan is not a separate unit, it's just a limited release model for Yuan Yuans. Outrage characters other than Knauf are not available in default ITS missions, so that's probably the reason they never bothered to include them in Army.