I'm not 100% sure how these cards work. Does Imbued Vitality basically turn all Ongoing and Equipment cards into Targets, which as a result can be eaten by Raptors, shot by Assault Rifles, etc.?
Ghostly Images can put One-Shots in play. Does putting a One-Shot in play have any effect?
Imbued Vitality: Yes, that is exactly how the card works.
Ghostly Images: A little awkwardly worded, but yes, the effect of the One-Shot happens (Putting Fire Blast into play means Ra deals 1 target 5 fire damage).
The important difference to realize is that you can "put a card into play" even when you can't "play cards," so you can use it even when an environment says you can't. On the other hand, Take Down (non-EE, at least) doesn't prevent Omnitron repairing drones or the Operative summoning underbosses.
Quotes for emphasis because i can teh grammerz
What happen when Imbued vitality leave play ? or when another ongoing enter play ?
If IV leaves play they ongoings lose their 'target' status and revert to 'ordinary' ongoing cards.
If another ongoing enters play it is affected by IV and becomes like all the other ongoings/equipment out there, a target with 6HP as well as its base type.