[Starscream Gaga]

I don't think they'll use the other Sentai. Considering that 52 episodes with usually about 3 Gokai Changes an episode, they have plenty of footage of every team to display. It also helps that after Gokai Silver joined pre-Zyu Gokai Changes became a bit less common because there weren't enough members compared to Gokaiger.

However, I think its definite they won't bother to hide the Sentai in the Legend War. I know they've filmed some extra footage, but this is Saban and I think the temptation to just mostly copy paste the Sentai footage will be too much. I expect to see a lot of Sentai in the background, just like we've seen in Megaforce.